USDM 2.5L Speed Density Guide - Cobb Tuning

SUBARU ACCESSTUNER SOFTWAREUSDM 2.5L Speed Density GuidePrepared by: COBB Tuning Calibration and Engineering TeamsDocuments Available:USDM Subaru Tuning GuideUSDM 2.5L Speed Density GuideUSDM 2.0L Speed Density GuideUSDM Subaru Monitor DescriptionsUSDM Subaru Table Descriptions

SUBARU SPEED DENSITY 2.5L GUIDEVersion 1.311/21/2012

Table of ContentsOverview .................................................................................................................................................................................... 5Uses ............................................................................................................................................................................................ 5Supported Vehicles List .............................................................................................................................................................. 5Glossary of Acronyms ................................................................................................................................................................. 6Features ...................................................................................................................................................................................... 6Hardware Requirements ............................................................................................................................................................ 7Warnings .................................................................................................................................................................................... 8OFF-ROAD USE ONLY ........................................................................................................................................ 8READ ALL DOCUMENTATION BEFORE TUNING .............................................................................................. 8SD IS NOT FOR INEXPERIENCED SUBARU TUNERS ..................................................................................... 8VERIFY FACTORY AIRFLOW AND LOAD LIMITS AND RAISE AS NEEDED ..................................................... 9MANIFOLD PRESSURE SENSOR CHECK ENGINE LIGHT ERRATIC LOAD CALCULATION .......................... 9ENGINE HARDWARE CHANGES MAY REQUIRE A RE-TUNE FOR SD ............................................................ 9POTENTIAL RISKS FOR SD WITH A HEAT SOAKED IAT SENSOR .................................................................. 9SD Installation Steps ................................................................................................................................................................. 10What is Speed Density? ............................................................................................................................................................ 11What is Volumetric Efficiency? ................................................................................................................................................. 11Volumetric Efficiency Table ...................................................................................................................................................... 12SD Modes ................................................................................................................................................................................. 12Tuning SD – Mechanical Configuration ..................................................................................................................................... 13Tuning SD – Getting Started ...................................................................................................................................................... 13Tuning SD – Initial Map Configuration ...................................................................................................................................... 13Airflow and Load Limits .................................................................................................................................................... 13Manifold Pressure Sensor Diagnostic Trouble Codes ........................................................................................................ 14Load and MAF Compensation ........................................................................................................................................... 15Conservative Fuel and Timing Maps ................................................................................................................................. 15Fuel Injector Scale and Latency ......................................................................................................................................... 15Engine Displacement ........................................................................................................................................................ 16VE Table Axis Scaling ......................................................................................................................................................... 16Reflash Changes ................................................................................................................................................................ 16Copyright © 2012 COBB Tuning Products LLC. 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Row/Column Table Data and Dynamic Advance Tables Removed from Real-Time .......................................................... 35Other Changes to Real-Time ............................................................................................................................................ 35Real-Time Tunable SD Tables ............................................................................................................................................ 35SD Airflow Math ....................................................................................................................................................................... 36Ideal Gas Law – Introduction ............................................................................................................................................ 36Ideal Gas Law – Real-World Inputs ................................................................................................................................... 36Ideal Gas Law – Volumetric Efficiency ............................................................................................................................... 37Ideal Gas Law – Mass Airflow ........................................................................................................................................... 37Ideal Gas Law – SD Reference Airflow .............................................................................................................................. 38SD Final Airflow ................................................................................................................................................................. 38Estimated VE Calculation .................................................................................................................................................. 40Appendix – Aftermarket IAT Sensor Install ............................................................................................................................... 41Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 4

INTRODUCTIONNote: This guide covers COBB Speed Density for the USDM 2.5L Subarus. For information pertaining to the 02-05 USDM 2.0L WRX, please see our 2.0L Speed Density guide.OverviewThe COBB Speed Density feature is a powerful yet easy-to-use solution that integrates Speed Density tuning intothe Subaru engine control unit (ECU) and can be used to entirely replace or work in conjunction with the existingfactory mass airflow (MAF) sensor. It is highly customizable and features such as real-time tuning aid in a speedyand efficient tuning process.UsesCOBB Speed Density (SD) has a number of potential uses that can improve the tuning capability for particularset-ups:• SD can eliminate the noisy airflow calculation sometimes seen when using a MAF sensor-based configurationwith heavily modified cars.• SD allows for the MAF sensor to be removed, eliminating a potential restriction in the intake tract and allowingfor more freedom in intake piping design.• In a special hybrid mode, SD can be used on the high end to overcome a maxed out MAF sensor, whilestill retaining MAF sensor operation on the low end. Or SD can be used on the low end to improveidle/cruise characteristics when a big MAF is used, while still retaining MAF sensor operation on the highend.Supported Vehicles ListThe following vehicles designed for and sold in North America are supported:• 2006-2013 Subaru Impreza WRX• 2004-2013 Subaru Impreza STI• 2009-2010 Subaru Impreza 2.5GT• 2004-2013 Subaru Forester XT• 2005-2012 Subaru Legacy GT• 2005-2009 Subaru Outback XTCopyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 5

Glossary of Acronyms• ECT = Engine Coolant Temperature• ECU = Engine Control Unit• IAT = Intake Air Temperature• IC = Intercooler• MAF = Mass Airflow• MAP = Manifold Absolute Pressure• RPM = Revolutions Per Minute (referring to engine speed)• SD = Speed Density• VE = Volumetric Efficiency• WBO2 Sensor = Wideband Oxygen SensorFeaturesThe following is a list of the key features of COBB Speed Density (SD):• SD works by calculating a new SD-based airflow to replace the factory MAF sensor-based airflow whenSD is active. This keeps much of the existing factory logic in place, allowing for the safe and reliable operationof the factory ECU while reducing the learning curve associated with tuning SD.• Adding the SD functionality to your existing COBB maps is a simple as opening the map in the Access-TUNER software with the SD ECU selected, saving the map, transferring the map to the AccessPORT,and reflashing the map to the car. From there, you simply start tuning with the AccessTUNER software.• Tuning SD is achieved through manipulating a real-time tunable volumetric efficiency (VE) table. Becausethe VE table units represent actual VE, properly calibrated SD tunes can be used to compare VE acrossdifferent cars with different mods, even if the SD airflow is drastically different.• A real-time tunable intake air temperature (IAT) compensation table allows the tuner to tweak the SDcharge temperature correction. This table can be tweaked according to manifold pressure, allowing forchanges that may be needed based on IAT sensor placement. SD airflow compensations for enginecoolant temp (ECT) and barometric pressure are also available.• Tuners can select from three different real-time tunable modes of operation. MAF mode mimics the factorylogic in which airflow is determined by the MAF sensor and the “MAF Calibration” table. This mode allowsyou to get a starting VE table up and running before actually running SD or allows you to tune MAFsensor calibration as you would with the factory ECU. SD mode is full-time SD operation where the ECUuses the SD-based airflow calculation. Hybrid mode allows for switching between MAF and SD modeCopyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 6

(and vice versa) based on thresholds of throttle, RPM, MAP and MAF voltage. During the transition, theMAF sensor and SD-based airflow calculations will be blended over a short period of time to allow for asmooth transition between modes. The speed of this transition and how the switching takes place can alsobe configured.• The SD and MAF sensor-based calculations are made regardless of mode. This means that the MAFsensor-based airflow can be compared to SD airflow regardless of which airflow value is currently beingused.• For cars with a properly calibrated and installed MAF sensor, an available estimated VE monitor can beused to more quickly get the initial tune for the VE table up and running. This can even be done in MAFmode, where the VE table (and other SD elements) can still be tuned before actually running SD.• Because the response characteristics of the MAF sensor (used in MAF mode) and the MAP sensor (usedin SD mode) are different, a tunable load smoothing factor is available for each mode. This determineshow load is filtered by the ECU and allows for better idle and tip-in/tip-out behavior in SD mode, while retainingthe correct filtering in MAF mode.Hardware RequirementsThe following minimum hardware requirements must be met in order to use the SD feature:• MAP Sensor - The manifold absolute pressure (MAP) sensor installed in the car must be accurate, reliable,and capable of reading boost greater than the car can ever achieve. A typical car that would necessitatean SD tune would likely max out the factory MAP sensor and require an aftermarket MAP sensor tobe installed. Any aftermarket MAP sensor must be properly scaled in the map (via “MAP Sensor Calibration(Offset)” and “MAP Sensor Calibration (Multiplier)” tables) and its accuracy should be verified by anexternal boost gauge before tuning SD. Note: A MAP sensor related check engine light can cause afailsafe load calculation to come into play, potentially causing issues when SD mode is active (please see“Tuning SD – Initial Map Configuration” section for more details).• IAT Sensor - Vehicle must have a working, accurate and properly calibrated intake air temperature (IAT)sensor. The IAT sensor is crucial to the SD airflow calculation. The SD airflow calculation relies on a theoreticalinput of the cylinder charge temperature. The closer the IAT reading is to the actual cylindercharge temperature, the more accurate (and consistent) the SD airflow calculation will be and the easierSD will be to tune. The factory IAT sensor is in the MAF sensor assembly in a draw-through configuration(i.e. pre-turbo). While it is possible to tune SD with an IAT sensor in this location, it is more difficult and willrequire more tweaking of the SD IAT compensation table (because this placement does not take into considerationturbo and intercooler efficiency). We recommend that the IAT sensor be placed post-intercooler,if possible. This could be using the factory MAF/IAT sensor assembly moved to a blow-through configuration(i.e. post-front mount intercooler) or an aftermarket IAT sensor placed in the intake piping in the samelocation (see appendix for details on how to install an aftermarket IAT sensor). Keep in mind that an aftermarketIAT sensor will require a different calibration that the factory IAT sensor.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 7

• Other Sensors - Any sensor or component necessary for the operation of the factory ECU must be working,installed, and properly calibrated. The only exception is the MAF sensor assembly if the tune is set torun only in full-time SD mode (see “MAF Sensor Removal” below).• MAF Sensor - The MAF sensor assembly must be installed and properly calibrated if the MAF mode, hybridmode, or estimated VE monitor is to be used. It must also be installed if the factory IAT sensor (whichis part of the MAF sensor assembly) is to be used for SD (rather than an aftermarket IAT sensor).• MAF Sensor Removal - If the MAF sensor is removed, disconnected, or otherwise non-functional, you willonly be able to run the car in full-time SD mode and the car will not start or run when MAF mode is active.You will also need to disable any MAF sensor related diagnostic trouble codes (DTCs) such as P0101,P0102, and P0103. While the ECU’s primitive failsafe load calculation has been disabled in the COBB SDECU, disabling the MAF sensor DTCs is still necessary because other fail-safe logic can come into play.Also, removal of the factory MAF sensor assembly also removes the factory IAT sensor requiring you to installan aftermarket IAT sensor.• Wideband Oxygen Sensor - A properly functioning and installed wideband o2 (wbo2) sensor is necessaryto tune SD. It is also highly recommended that a permanently installed wbo2 sensor with an interior gaugeis used so that the driver can monitor fueling after the tune is complete.• Mechanical Issues - Any mechanical problem with the car needs to be addressed before attempting totune SD.WarningsOFF-ROAD USE ONLYSome or all of the features and modifications discussed in this guide may not be legal to use outside of off-roadracing applications. Always consult local, state and federal laws to determine what is legal for your particular situation.READ ALL DOCUMENTATION BEFORE TUNINGCOBB SD for Subarus has been designed with the purpose of coming up with the best implementation for theunique attributes of the Subaru ECU, while allowing for an easy conversion to SD for existing MAF sensor-onlymaps. COBB SD is not like other SD systems that you may be familiar with, including even COBB implementationsfor other platforms. As such, it is critical that you read through this guide and understandhow COBB SD for 2.5L Subarus works before attempting to tune. If you have any questions, we are alwayswilling to help.SD IS NOT FOR INEXPERIENCED SUBARU TUNERSThere are many unique qualities to Subaru ECU logic that can make it challenging for someone new to the platform.If you are new to Subaru tuning, it is recommended that you first become proficient at tuning MAF sensoronlyset-ups before tackling SD tunes. MAF sensor-only tuning can be much more forgiving to mistakes than SDtuning.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 8

VERIFY FACTORY AIRFLOW AND LOAD LIMITS AND RAISE AS NEEDEDIt is important to understand that the factory airflow and load limits are still applied even when the SD-based airflowis being used. Please see “Tuning SD – Initial Map Configuration” section for more details. Failure to raisethese limits appropriately could result in engine damage as the calculated airflow and/or load becomes static pasta certain point.MANIFOLD PRESSURE SENSOR CHECK ENGINE LIGHT ERRATIC LOAD CALCULATIONAny diagnostic trouble code (DTC) related to the manifold pressure sensor will cause the Subaru ECU to estimatemanifold absolute pressure (MAP) based on the current calculated load (as a failsafe). This can result in an erraticload calculation in SD mode because actual MAP (a key input for SD) would no longer be determined correctly. Ifthis occurs when the vehicle is accelerating, a lean condition and incorrect timing can result. It will also likelycause the engine to eventually stall. If there is the possibility that any of the MAP sensor related DTCs (P0068,P0107, or P0108) could be triggered, it is critical that those DTCs are disabled in the tune. The installation of anaftermarket MAP sensor (required for SD if the factory MAP sensor is not sufficient) will make it more likely forthese DTCs to be triggered, even though there may be nothing wrong with the sensor itself. Please see “TuningSD – Initial Map Configuration” section for more details.ENGINE HARDWARE CHANGES MAY REQUIRE A RE-TUNE FOR SDIt is important to understand that after the SD tune is complete for a given car, any further changes to enginehardware that impacts airflow efficiency in or out of the engine can potentially require tweaking or re-tuning of theVE table to avoid fueling/timing issues (due to incorrectly calculated SD load). Additionally, mechanical issues,such as intake/exhaust leaks, and issues related to the aging of the motor, such as combustion deposits and lossof compression, can also impact actual VE. It is highly recommended that a permanent wideband o2 sensor andgauge is installed in the vehicle and that the driver understands how to read the gauge and determine what is normalfor their tune.POTENTIAL RISKS FOR SD WITH A HEAT SOAKED IAT SENSORAny SD calculation, including COBB SD, requires an input for cylinder charge temperature, which is critical to thedetermination of accurate airflow via SD. The estimation of cylinder change temperature is accomplished forCOBB SD via the IAT sensor input. Generally, when the IAT sensor is in the recommended location (post-IC), thevehicle is moving and the driver is on the throttle, the IAT input can be a fairly reliable representation of actual cylindercharge temp. However, when the vehicle is sitting still (or at low speeds) and the driver is off the throttle (orlow throttle), or the vehicle has been sitting with the engine off and a hot engine bay for a period of time, there isthe potential for the IAT sensor to become heat soaked. That is, the sensor now reads higher than the actual intakeair temp. When SD is active, this would cause the calculated SD airflow (as well as load) to be lower than itshould be, causing the car to run lean (and with generally more timing advance). This effect may subside after thevehicle gets moving and throttle (as well as MAP) increases, but it will generally not be an instantaneous improvement.As such, it is critical that the owner/driver of the car understands the specific scenarios in which a heatsoaked IAT sensor can potentially occur and to avoid putting the car under high load when these scenarios arepresent (and for a period shortly after). This is another reason why a wideband o2 sensor and gauge should be installedin the car and that the driver instructed on how to determine when fueling is incorrect.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 9

INSTALLATIONSD Installation StepsBefore tuning with SD, you’ll first need to update your AccessTUNER software and AccessPORT firmware to versionscompatible with the SD feature as follows. Always make sure to periodically check for future updates.1. If your current AccessTUNER version has the auto updater feature, you can update the software to the SDversion via the internet (“Help” -> “Check for Updates”). If your version does not have auto-updater, youwill need to download or submit a request for a new version:For AccessTUNER Pro, you can find the latest version here:http://www.accessecu.com/support/TunerPro_Suba_Setup.exeFor AccessTUNER Race, you can submit a request for the latest version here:http://www.cobbtuning.com/accesstuner-race-request-s/70716.htm2. Update your AccessPORT firmware to the latest version via the AccessPORT Manager software. The followingvideo shows you how to update your firmware:http://www.cobbtuning.com/AccessPORT-Support-s/40200.htm#/v/accessport/support-tutorialsfirmwareNow that your software and firmware is updated, you will need to reflash an SD-capable map to the car you willbe tuning:1. Run the AccessTUNER software and when prompted with the ECU selection dialog, make sure the“Speed Density” checkbox is checked. For AccessTUNER Pro, you will also need to select the ECU of thecar you wish to tune.2. You may now either open your existing map or simply use the default stock mapping in AccessTUNER.Make any initial changes to this map that you wish to start from for SD (see “Tuning SD – Initial Map Configuration”later in this document).3. Save your map. This map will now have the SD feature.4. Transfer the map to the AccessPORT with the AccessPORT Manager software.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 10

5. Reflash the new SD map to the car via the AccessPORT.6. The car is now ready to be tuned via SD.SD BASICSWhat is Speed Density?The Subaru ECU, as well as any engine management solution, needs to determine the mass of air entering theengine in order to determine the correct amount of fuel to inject for a given desired fueling target. With the SubaruECU, it is represented in terms of mass airflow (grams per second), which, along with engine speed (RPM), isused to determine load (grams per crankshaft revolution). For the Subaru ECU, load is not only used to determinethe proper injector pulse width, but also the desired fueling/timing targets. The modern factory Subaru determinesmass airflow via the mass airflow (MAF) sensor. The MAF sensor-based system attempts to directly measure theactual mass airflow (given the relationship between MAF voltage and airflow for a specific intake and sensor).Speed Density, on the other hand, attempts to estimate mass airflow via other inputs. The basis for this calculationis given by the ideal gas law. The ideal gas law is a relationship in physics between various inputs that allowsfor an estimation of the mass of an ideal gas. In our case, the ideal gas is the air entering the combustion chamberof the motor. The variables involved in the calculation (for COBB SD) include manifold absolute pressure(from the MAP sensor), cylinder charge temperature (i.e. approximated by our IAT sensor input), volumetric efficiency(from our VE calibration table), engine speed (RPM), and engine displacement (tunable parameter). Fromthis, an estimation of mass airflow can be made (see “SD Math” section for a detailed explanation of the math involved).What is Volumetric Efficiency?Simply put, it is the amount of air inducted into the engine relative to the engine’s displacement. An engine is essentiallyan air pump and volumetric efficiency (VE) defines how efficient that process is. A volumetric efficiency of100% would indicate that the amount of air inducted is the same as the engine displacement (at standard conditions)for a given engine cycle. If all engines always operated at 100% VE, there would be no need to account forVE in determining the SD airflow. But, this is far from the case.Numerous factors impact how VE varies with conditions for a given engine. As far as engine hardware, this caninclude, but not limited to, the entire intake tract (from air filter to turbo to intercooler to throttle body), all exhaustcomponents, intake manifold design, cylinder head design, intake/exhaust valve design, compression ratio, camshafttiming and lift (including variable valve timing via tuning), and so on.Mechanical/aging issues, depending on their severity, can also potentially impact VE. Examples would includecombustion deposits, intake/exhaust leaks, and loss of engine compression.Among engine operating inputs, VE is most likely to change according to manifold absolute pressure (MAP) andengine speed (RPM). This is why the VE table uses MAP and RPM axes (as is typical with most SD solutions).Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 11

Volumetric Efficiency TableThe VE table is the primary means by which an SD tune is accomplished for a given car. Once tuned, changes toengine hardware and/or mechanical/aging issues that arise (as described in the section above) may require retuningof the VE table. What areas of the table that need to re-tuned or tweaked is going to depend on the changeitself and how it impacts actual VE across a range of MAP and RPM.Tuning the VE table is simply determining the actual VE so that the SD airflow is as close to the actual airflow aspossible. This can be accomplished by comparing the ECU’s fueling target with actual fueling (via wideband o2sensor). All things being equal, increasing VE in the VE table will result in an increase in SD airflow (for theMAP/RPM area impacted). This will result in an increase in load and fueling will become richer. On the otherhand, decreasing VE in the VE table will result in a decrease in SD airflow. This would have the opposite effectwith load decreasing and fueling becoming leaner. Keep in mind that because load is also used as an input to ignitiontiming, cam timing (AVCS), and the primary fuel tables (among other tables), the change in load will also impactthe desired targets for these tables.Generally speaking, the peak VE for a given column of the VE table will generally occur at the RPM of the motor’speak torque and VE will progressively drop on either side of that RPM point. Also, VE generally tends to increaseas MAP increases. Keep in mind that these are not hard and fast rules. You may find that the VE tune necessaryfor a given car does not follow these guidelines completely.SD ModesCOBB SD gives you the option of running several different modes that determine how airflow will be calculated.The modes are determined by the following “SD Mode” table:MAF mode – A value of 0 in this table will enable full-time MAF mode. This results in airflow being determined exactlyas the factory ECU logic dictates. That is, airflow is determined based on MAF sensor input and the “MAFCalibration” table. This requires that the MAF sensor is still installed, functional and properly calibrated. In thismode, the SD airflow will still be calculated even though it is never used. This will allow you to compare the SDairflow to the MAF sensor-based airflow via the “SD Airflow (Post-Comp)” and “Mass Airflow (MAF Calibration)”monitors. In addition, you can also tune the SD tables in this mode. The “SD VE Estimated (MAF)” monitor (whichis available in any mode) will estimate VE based on the MAF sensor-based airflow (and other inputs) which youcan use as reference to get an initial tune of the VE table started. In MAF mode, this will allow you to makechanges to the VE table while still running the MAF sensor-based tune.SD mode – A value of 1 in this table will enable full-time SD mode. That is, the airflow normally determined by the“MAF Calibration” table in the factory ECU will always be replaced by the SD airflow calculation determined byyour SD tune. Even though the MAF sensor-based airflow will not be used by the ECU in this mode, you can stillmonitor/log this value via the “Mass Airflow (MAF Calibration)” monitor. If the MAF sensor is still installed, func-Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 12

tional and properly calibrated, you can use this value as a comparison to the SD airflow determined by your SDtune.Hybrid mode – A value of 2 in this table will enable hybrid mode. This allows you to switch to either MAF or SDmode based on a series of tunable thresholds for throttle, RPM, MAP and MAF voltage. That is, you can decidewhen the ECU will use the MAF sensor-based airflow and when it will use the SD calculated airflow. When transitioningbetween MAF and SD mode (or vice versa), the current airflow will be a blend of the two mode calculationsto allow for a smooth transition. The speed of this transition can be tuned.SD TUNINGTuning SD – Mechanical ConfigurationBefore jumping in and starting tuning, make sure the car meets the minimum hardware requirements outlined inthe “Hardware Requirements” section found earlier in this document. Failure to do so can result in an inconsistenttune as well as potential engine damage.Tuning SD – Getting StartedInstalling SD – Make sure an SD map has been reflashed to the car’s ECU and you have the latest SDcapablesoftware and firmware updates as outlined in the “SD Installation” section earlier in this document.Opening Map – Run the AccessTUNER software, select the “Speed Density” checkbox, and select theECU of the car you are tuning. Open the SD map you reflashed to the vehicle.Tuning SD – Initial Map ConfigurationAirflow and Load LimitsBecause most of the factory logic is retained for COBB SD, factory limits that cap airflow and load are still applied.It is critical that these limits are double checked for your tune. Otherwise, it could cause a dangerous lean conditionwhere the calculated airflow/load is capped even though actual airflow/load is still increasing. This is true regardlessof whether SD airflow or MAF sensor-based airflow is being used. The following outlines how to checkand raise the airflow/load limits:Raising Factory Airflow Cap – This is as simple as raising the value in the “MAF Limit (Max)” table, locatedin the “Miscellaneous Limiters” table group. This should be raised to a value that the car will never hitunder any circumstances. For SD ECUs, the default for this table has been raised to 2000 g/s (from thefactory 300 g/s), although this can be overridden by the map you are opening, so be sure to double-checkthis limit.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 13

Raising Factory Load Cap – If the ECU you are tuning only has a single load limit table (“Load Limit(Max) Primary” under the “Miscellaneous Limiters” group), then raising the load cap is as simple as raisingthe value in this table. If, however, the ECU has the second load limit table (“Load Limit (Max)Secondary”), the process is more involved. First, raise the “Load Limit (Max) Primary” to your new limit.Second, raise all the “Load Limit (Max) Secondary” load values to their max of 4.0 g/rev. Third, raise all the“Load Limit (Max) Secondary Compensation (Barometric)” values to 100%. Do the same for “Load Limit(Max) Secondary Compensation (Intake Temp)” table. The 100% compensation across both tables willresult in doubling the secondary load limit twice. For example, if the secondary load limit was 4.0 g/rev, thenew load limit (with 100% in all cells of secondary compensation tables), would be 4 * 2 * 2 = 16 g/rev.Manifold Pressure Sensor Diagnostic Trouble CodesIf a check engine light is set related to the manifold absolute pressure (MAP) sensor, the ECU will switch to an alternatefailsafe calculation for manifold pressure based on load. Because MAP is a key input to the load calculationin SD mode, this results in a feedback loop in which actual MAP no longer plays a role in determining SDload. This erratic load calculation could cause a dangerous lean condition (with incorrect timing), if actual MAP isincreasing at the time (for example, if the vehicle were accelerating). It will also likely cause the car to eventuallystall.One or more of the MAP sensor diagnostic trouble codes (DTCs) can even be set when there is no actual failureof the MAP sensor. This can occur in the following circumstances:• High level of boost (i.e. MAP voltage) is seen by the factory or aftermarket MAP sensor that exceeds thefactory DTC limits.• Lower level of MAP voltage due to aftermarket MAP sensor’s expanded relative range.The following are the MAP sensor related DTCs in question:• P0068 - Manifold Absolute Pressure Circuit Range/Performance Problem• P0107 - Manifold Absolute Pressure Circuit Low Input• P0108 - Manifold Absolute Pressure Circuit High InputIt is critical that if the possibility exists that any of these DTCs may be set, they should be disabled for the SDECU. This can be accomplished by unchecking these DTCs in the “Edit” -> “Advanced Parameters” menu, savingthe map, and then reflashing the map to the ECU.For the P0107 and P0108 codes, the DTC voltage limits can be configured in the AccessTUNER software via the“MAP Sensor Voltage DTC Limits (High/Low)” table (found in the “Boost Control Tables” -> “Boost Limiters”group). Additionally, the “MAP Sensor Voltage DTC Delays (High/Low)” table determines how long the voltagelimit must be exceeded before the DTC is set. Both of these tables can be used in place of disabling these twoDTCs if a proper range can be determined. For the SD ECU, the defaults of these values have been expanded,although this can be overridden by the map that is opened. Keep in mind that the P0068 DTC limit is not configurable.This DTC is set when MAP voltage is not above a specified threshold given specific conditions related toRPM, throttle, and load.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 14

Load and MAF CompensationIn addition to the airflow/load limits, the factory airflow/load compensations are still applied to the SD-based andMAF sensor-based airflow/load calculations. It is important to look at and understand these compensations asthey will ultimately determine the final airflow and load that is used:• MAF Compensation - The airflow compensation table is called “MAF Compensation (Intake Temp)” andcan be found under the “Sensor Calibrations” group. This determines the compensation to airflow basedon IAT and current airflow. Generally speaking, this compensation is not needed for SD tunes (some ECUshave this zeroed-out from the factory to begin with). If you are running in hybrid mode, you can retain thecompensations when MAF mode is active by separately manipulating the compensations above and belowan airflow breakpoint in the table that would represent the approximate switchover point of your hybridtune for MAF to SD (and vice versa).• Load Compensation - The load compensation table is called “Load Compensation (Manifold Pressure)”.This determines a compensation to load based on MAP and RPM. There may be multiple tables dependingon the ECU. The factory load compensations should not be needed for the SD tune. Because this tableuses MAP and RPM axes (same as the VE table), any corrections to load necessary can be accomplishedvia the VE table for the SD tune and therefore, the load compensation tables can be zeroed-out. However,as it relates to correcting the 08+ STi “stumble” issue, you may find it easier to leave the factory compensationsin place as this may result in a more predictable starting point for the VE tune (although this is notrequired). If you are running hybrid mode and need to retain the corrections when MAF mode is active,you can set up hybrid mode to use a MAP threshold and then manipulate the load compensation table(s)appropriately.Conservative Fuel and Timing MapsIt is important to consider using conservative fuel and timing maps during the initial SD tuning phase. When startingyour tune, the VE table will not be perfect until you’ve had a chance to dial it in. While you are tuning the table,any error from actual VE will not only result in the incorrect fueling, but also the incorrect load values. If the VE fora given cell in your table is less than actual VE, this will result in load that is less than actual load. Because thetiming tables (“Primary Ignition” and “Dynamic Advance”) use load as an input, the timing advance will generallybe higher than intended in this case. The primary fuel table(s) also use load as an input and the desired fuelingtarget will generally be leaner than intended in this example. This issue would also impact the cam timing (AVCS)table(s) as well as any other table that uses load as an input. If the VE for a given cell in your VE table is greaterthan actual VE, the opposite will occur, where load will be greater than actual. This is why you generally want tobias your VE values to a higher estimation of VE when starting out, rather than a lower one.Fuel Injector Scale and LatencyTuning for new injectors for COBB SD is no different than the factory MAF sensor-only process. As such, you willneed to make sure your fuel injector scale and latency values are tuned correctly prior to tuning with SD. If youare changing injectors at the same time as changing over to SD, you’ll need to at least make sure that you havereasonable starting values for the new injectors.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 15

Engine DisplacementCOBB SD uses engine displacement as one of the inputs to the SD airflow calculation. As such, this requires thatyou input the correct displacement of the motor you are tuning via the “SD Engine Displacement” table (under the“Speed Density” table group). This should be the closest value (in liters) to the car’s actual engine displacement.The default value is 2.457 liters, which is the closest actual displacement to the factory 2.5L USDM turbo motor.VE Table Axis ScalingThe default values for the MAP axis of the VE table is in 2 psia steps up to a maximum of 44 psia and the defaultvalues for the RPM axis is in 350 RPM steps up a max of 7700 RPM. You need to make sure that the maximumvalues are enough for the max MAP and RPM that the motor will likely see. When either RPM or MAP exceedstheir corresponding max axis values, the ECU will continue to use the VE values in the last row (or column). If youneed to make a change, simply re-scale the axis values and reflash those changes to the ECU. Keep in mind thatthe MAP axis is in units of manifold absolute pressure, not relative pressure. If you wish to determine the correspondingrelative pressure values (for reference) simply subtract your barometric pressure from MAP. The barometricpressure can be read via the “Barometric Pressure” monitor. If you are at/near sea level (barometric pressurearound 14.7 psi) and you wish to quickly determine the relative pressure in your head, simply subtract 15 psifrom the MAP axis value you are looking at (for example, 30 psia – 15 psi = 15 psig). This will give you a quick approximationwhen you wish to think in terms of relative pressure.Reflash ChangesMake sure you save this map with the initial changes and reflash to the car before continuing with the tune.Tuning SD – Starting Values for the VE TableThe default values for the VE table are set to 100% across the entire table. This is not meant to be a starting pointto run the vehicle in SD mode and tune. Instead, you want to consider coming up with initial values in the VE tablethat are reasonable enough to run the car in SD mode. The following gives suggestions based on whether or notthere is a functional MAF sensor installed in the car.Car with Working and Accurate MAF SensorIf the car has a properly functioning and calibrated MAF sensor installed, you can use the “SD VE Estimated(MAF)” monitor to aid in determining starting values for your VE table. If there are issues with the accuracy of theMAF sensor (and resulting airflow calculation) or problems with the IAT sensor, MAP sensor, and/or engine displacementinputs, this will impact the accuracy of the estimated VE monitor. Also, because MAF sensor-based airflowtends to be overestimated on throttle tip-in and underestimated on throttle tip-out, the estimated VE monitorwill also be inaccurate during these periods.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 16

The idea here is that you will be tuning your starting VE table while remaining entirely in MAF mode. That is, if thecar you are tuning runs well in MAF mode, you can get a decent initial set-up for the VE table before actually runningthe car in SD mode. In addition to the estimated VE monitor, you can also view/log the “SD VE (Commanded)”monitor, which is the current VE table look-up. This is VE based on the VE table that would be used inthe SD airflow calculation if SD mode was active. By comparing the estimated VE and commanded VE, you cantweak the VE table appropriately. Keep in mind that the estimated VE monitor is not a substitution for actually tuningthe VE table in SD mode based on actual fueling.There are a handful of methods you can use to take advantage of the estimated VE monitor in order to come upyour starting VE tune in MAF mode. You may find some or all of these are useful, depending on what tools youhave available and the time you have to spend with the vehicle:• Data logging – One way to come up with reasonable initial VE values for specific MAP and RPM areas ofthe VE table is via data logging. You’ll need to at least log the “SD VE Estimated (MAF)”, “Manifold Abs.Pressure”, “Engine Speed”, and “Throttle Position” monitors. Logging throttle position will allow you to filterout the inaccurate estimated VE values when throttle is rapidly changing (ex. during tip-in and tip-out).With data logging, the more data points you have for a given MAP/RPM range, the more accurate your estimationof VE will be as it will allow you to throw out more extreme values. But, you should keep yourstarting VE values towards the higher side to reduce the chances of a VE error in the starting map resultingin a lean condition when you start to tune in SD mode. Keep in mind that if the IAT sensor becomesheat soaked, which may occur with extended idling and stop and go driving, the estimated VE monitor willoverestimate VE compared to actual. You may want to also log “Intake Temperature” and “Vehicle Speed”so you can see if there’s any relationship between a higher estimated VE and the conditions that may resultin a heat soaked IAT sensor. As you accumulate data, modify the VE table appropriately and then addthe “SD VE (Commanded)” monitor for additional logging. You can then compare your table VE to estimatedVE so you can tweak VE further.• Steady-state tuning on dyno – If you are tuning on a load-bearing dyno, you can also hold cells of theVE table and come up with an initial VE for a given cell based on the estimated VE monitor. This would beaccomplished by enabling live tracing on the table and taking advantage of real-time tuning. As you viewthe estimated VE monitor, it will show a range of values as the inputs to this calculation rapidly change. Tryto use the highest reasonable value shown. It is not realistic to attempt to do this for every cell of the tablejust for an initial VE pre-tune. But, you could focus on, for example, the RPM row that is likely to be closestto peak torque and, therefore, where VE is likely to be highest (for a given MAP column).• Filling in the blanks – Depending on the time available for the tune, it may not be feasible to try to estimatethe majority of the cells in the VE table using the methods described above. Instead, you can focus onmore narrow portions of the map representing low, mid and high MAP areas and then “fill in the blanks”between these areas. Generally speaking, as MAP increases, VE also increases. Also, as it relates toRPM, VE will tend to follow the torque curve of the motor, generally peaking at the same RPM as the peaktorque of the motor. These are not hard and fast rules, but they are sufficient enough to allow you to interpolatebetween the areas of the map you have worked on for the starting VE tune. Keep in mind that theWOT area of the VE table (i.e. high MAP) is going to be the most crucial area of your pre-tune. This is becauseload errors at high MAP have the most potential to cause engine damage. You do not want your firstWOT pull in SD mode to result in an overly lean condition with more timing advance than anticipated. ThisCopyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 17

is also a reason to go with more conservative fuel and timing maps until you get the VE table dialed-inafter switching to SD mode.Once you have a reasonable starting VE table, you may want to consider bumping up the values in the entiretable just to make sure your pre-tune is more likely to overestimate VE than to underestimate it.Car without Viable MAF Sensor ConfigurationIf the MAF sensor has been removed from the car or is otherwise inaccurate, inoperable or not properly calibrated,then there is not a means to directly estimate VE for a given car. Over time, however, you will see specificpatterns in the VE table for cars you’ve tuned (for a given set of mods) and setting up a reasonable starting VEtable for similar vehicles will not be difficult. If you have no frame of reference, however, you can start with somegeneral guidelines. The default values in the VE table will be 100% for all cells. This will be generally too high inthe lift-throttle, idle, and cruise areas (i.e. much too rich). Generally speaking, you may see more like 50%-60% inlift-throttle/idle areas and 60%-80% in cruise areas. Moderate boost may be in the 80%-90% range. Higher boostmay be in the 90% to over 100% range. To stay on the conservative side of things with your starting VE table, youwant to bias your estimate towards higher values rather than lower. This will reduce the chance of a lean conditionwhen the table VE is less than actual VE. This is especially critical at higher boost where a lean condition (andgreater timing advance) due to lower than actual load would be more of a problem.Tuning SD – The Tables“SD Volumetric Efficiency” TableThe “SD Volumetric Efficiency” table is the primary means by which the SD tune is accomplished. Once you haveyour starting values configured for this table (as described in the previous section), you can get to the actual tune.You’ll need to make sure you are in SD mode (1 in the SD mode table) and that the car is at operating temperature.As you hit the MAP/RPM area corresponding to a given cell, if your wideband o2 (wbo2) sensor reads richerthan what the ECU is targeting, you reduce VE for that cell. If your wbo2 sensor reads leaner than what the ECUCopyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 18

is targeting, you increase VE for that cell. You continue this process until you’ve dialed in as much of the VE tableas you can.The final ECU fueling target can be determined via the “Commanded Fuel Final” monitor. This may be different attimes than your primary open loop fueling map due to additional fueling compensations that come into play, suchas post-start/warm-up enrichment, long-term fuel trims, and others. Also, in closed loop, the ECU is not alwaystargeting 1.0 lambda (i.e. 14.7:1 AFR gas). The “Commanded Fuel Final” will account for all these changes as it isthe final fueling target used to ultimately determine injector pulse width.You should be aware of when the closed to open loop fueling transition occurs for your tune. When the transitionto open loop happens, you may see a lean or rich spike when the short-term fuel trims are no longer applied ifthat area of VE table needs work. You can determine the closed/open loop status via the “Closed/Open LoopSwitch” monitor.If the car has a functional and accurate front o2 sensor, you can also tune VE in closed loop via the short andlong-term fuel trims. Simply add together the “A/F Correction #1” and “A/F Learning #1” monitors and try to getthis sum as close to zero as feasible by manipulating VE. If the sum is positive, the ECU is adding fuel because ofa lean condition and you will need to increase VE. If the sum is negative, the ECU is removing fuel because of arich condition and you will need to decrease VE.You may be tempted to simply manipulate the VE table to hit the fueling target you desire for a given MAP/RPMarea regardless of the commanded fuel final (and the primary open loop fueling table). While this is certainly possible,it does have a few downsides. First, tuning this way would result in VE values that are not representative ofactual. That is, you could not easily compare them to other tunes. It can be quite useful to compare VE tablesacross tunes as it gives you an idea of VE changes with different mods (and cam timing). It can also help you usethose values as a starting point for new tunes for cars with similar mods. Second, making changes to fueling aftercompleting the tune is a little easier if the VE table represents actual VE. You would simply modify the primaryopen loop fueling table to your new desired open loop targets.When you’ve dialed in the VE tune, use the AccessTUNER graphing to help to smooth the table. Generally speaking,actual VE should not drastically change with small changes in RPM and MAP and, therefore, you should notsee drastic changes in VE between cells in the VE table. Smoothing the table will result in a more consistent loadcalculation and therefore, more consistent fueling and timing.In addition, you will also need to estimate the areas of the VE table you were not able to hit when tuning. The valuesshould be reasonable given the adjacent cells that were directly tuned. Also, keep in mind when estimatingVE, that VE will generally increase with an increase in MAP and for RPM, it will generally follow the torque curveof the motor (with the peak VE occurring at the RPM in which peak torque occurs and decreasing on both sides ofthat peak).Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 19

“SD Airflow Compensation (Intake Temp)” TableLike the VE table, the “SD Airflow Compensation (Intake Temp)” table is another critical component of the SD airflowcalculation. In order for our SD airflow to be accurate, we not only need to know MAP, RPM, VE, and enginedisplacement, but we also need to know the temperature of the cylinder charge. Without this input and its correspondingcorrection, any given cell in our VE table would only be valid at the charge temperature in which it wastuned. Without this correction, if the cylinder charge temp dropped from our tuned charge temp, we would go leanand if it went up, we would go rich.We have no means of directly measuring cylinder charge temperature so we have to rely on measuring intaketemperature at some point as a means of estimating charge temp. Generally, the closer to the combustion chamberwe measure the intake temp, the closer we’ll be to the charge temp. The Subarus we are tuning do not haveintake manifold temperature sensors, which would be the typical implementation for SD from the factory. Instead,Subarus have the IAT sensor housed in the MAF sensor assembly which is located pre-turbo in the intake tract.This is the only input that the factory ECU has for intake temp. In the case of a car with a front-mount intercooler,the MAF/IAT assembly could be relocated post-intercooler (or an aftermarket IAT sensor installed in the same location)which would give you a more accurate representation of charge temperature. Regardless, having the abilityto tweak the charge temp correction is an important component to the SD tune.Normally, if applying the ideal gas law to estimate engine airflow, the non-linear correction factor for charge tempwould be wrapped up in the ideal gas law equation. However, in order to allow the ability to tune this correction, ithas to be externalized. For COBB SD, this is accomplished by first calculating SD airflow at a specific referencetemperature of 86 degrees Fahrenheit. Then the “SD Airflow Compensation (Intake Temp)” is applied (along withthe other SD compensations) to determine the final SD airflow. As you can see from the default values in thetable, the 86 deg. F column has 0% correction. The default values for the rest of the columns are scaled with theideal gas law and our reference temperature in mind. As such, this allows for a tunable charge temp correction.What this all means is that there may be scenarios where your intake temp reading may be notably different fromthe actual charge temp. As such, the default ideal gas law based values in this table may need to be tweaked. Asyou can see, the table also has a MAP axis. This allows you to come up with different sets of corrections basedon MAP. This is important because MAP is one of the primary factors which can impact necessary tweaks to thetable. The default values for the MAP axis are mostly in vacuum, but these can be changed as needed (axis valuechanges require a reflash).One scenario in which the IAT reading may be notably different than the charge temp is when using an IAT sensorthat is placed before the turbo (known as a draw-through location). This is the case with the factory placed MAFhousing, which also contains the IAT sensor. When the IAT sensor is pre-turbo/intercooler, the impact of the turboand intercooler on charge temperature is not reflected in the IAT reading. Generally speaking, at very low MAP,Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 20

the effect is negligible. However, as MAP increases, you may find the need to tweak the IAT correction differentlybased on the input temperature and MAP. Keep in mind that heat soak of the IAT sensor (described below) mayalso be another factor that you would have to account for in addition to the pre-turbo IAT reading. This is why, ifyou are running a front-mount intercooler, we recommend that your IAT sensor be placed in a blow-through configuration(i.e. post-IC), whether than involves relocating the factory MAF/IAT assembly or wiring-in an aftermarketIAT sensor to the factory IAT input.The other scenario in which the IAT reading may differ markedly from actual charge temp is when the IAT sensorbecomes heat-soaked. What happens is that the sensor itself absorbs heat from the surrounding air and intakepiping and reads a temperature higher than the actual temperature of the airflow. Generally, this effect is progressivelymore pronounced at lower MAP/airflow and therefore you may be more likely to see it in conditionssuch as stop and go driving, extended idling, or a hot restart. Because the IAT reading is higher than the chargetemp, this would cause the airflow/load calculation to be less than actual and you would end up going lean (aswell as causing potentially more timing advance). When MAP/airflow does increase, the heat soak effect of thesensor does not instantaneously diminish, so the heat soaked reading may continue at higher MAP for a period oftime. This may present a problem if, for example, the car is subject to high loads (such as wide open throttle) soonafter heat-soak of the sensor sets in. This is one reason why a wideband o2 sensor and gauge in the car runningSD is important, as well as the driver understanding how to recognize a problem.There are some steps that can help partially mitigate specific heat soak scenarios. First is that the use of a shortramintake in a draw-through IAT configuration appears to be the combo where heat soak potential is the greatest.The post-intercooler IAT sensor placement appears to have the least heat soak potential (but can still definitelyoccur). Second is some tweaking of the IAT comp table may help in certain cases. Generally speaking, the higherthe IAT reading, the more likely heat soak of the sensor can occur. This may not always be the case, but it issomething you can attempt to mitigate by increasing the airflow compensation at higher IATs (i.e. higher correctionmeans higher airflow and more fuel). For example, you may find that the car becomes progressively leaner asIATs increase above 140F. In that case, tapering the negative correction progressively (from the default values) atIATs of 140F and greater could help. Also, the effect is likely to be more pronounced at lower MAP, so plan yourchanges accordingly. You may want to, however, keep some of your changes at higher MAP as the heat soak effectmay linger for a period in going from low MAP to high MAP. Keep in mind, though, that the heat soaked IATreading can potentially occur even at colder temps. For example, the charge temp may be 40 deg. F and the IATreading is 60 deg. F. This would still be a heat soak scenario (although one which would be difficult to account for)even though the temperatures are relatively mild.“SD Airflow Compensation (Coolant Temp)” TableCopyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 21

It is not necessary to tune the “SD Airflow Compensation (Coolant Temp)” table as far as the ideal gas law and ourSD airflow calculation is concerned. As such, the default values are set to 0% across the entire table. However,you may find some circumstances where it may be useful to tweak this table for your SD tune. One examplewould be more extreme coolant temp readings (on the high end). You may want to increase correction at this extremeas this may mean a more likely heat soak scenario for the IAT sensor (high ECT likely means higher radiantengine heat). As described in the previous section, a heat soaked IAT sensor (relative to actual charge temp) willresult in a lean condition with SD.“SD Airflow Compensation (Barometric)” TableAs you go up in altitude, the barometric pressure drops. The SD airflow calculation for COBB SD accounts for thischange because MAP is a part of the ideal gas law calculation and therefore, as barometric pressure decreases,MAP also decreases (all else equal) and SD airflow will also decrease. However, exhaust gas backpressure alsodecreases as barometric pressure decreases, which can impact VE. As such, you may need to tune the “SD AirflowCompensation (Barometric)” table if the car is going to see notable changes in altitude. In addition to the barometricpressure axis, this table also has a MAP axis. This will allow you to tune the compensation against MAPwhere the effect of exhaust gas pressure on VE may vary.Tuning SD – Miscellaneous TablesThe following are some miscellaneous SD-related tables that generally would not need to be tweaked for most SDtunes:Load Filtering in MAF and SD ModeCopyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 22

The factory ECU calculates a smoothed version of load for the final load calculation. Smoothing is a means of filteringout “noise” in a value by considering the change in the current value versus the previous value. That is, itwill tend to dampen larger short-term changes. The dampening effect is dependent on the smoothing factor usedin filtered calculation. The factory ECU’s load smoothing factor is set up for the response characteristics of theMAF sensor which is notably different than the MAP sensor, especially during transients. As such, the loadsmoothing is not optimal when calculating load based on SD airflow (i.e. when the primary input is the MAPsensor) and would potentially cause tip-in/tip-out and idle issues (among others) if not accounted for.COBB SD solves this problem by allowing for separate tunable load smoothing factors for SD and MAF mode.The smoothing factor is a value that ranges from above zero to 1.0. A value of 1.0 means that there is no smoothinginvolved and the load calculation is not manipulated. With values below 1.0, the smaller the smoothing factor,the more dampened the load will become. The “Load Determination Smoothing Factor (MAF Mode)” table, foundunder the “Speed Density” -> “Miscellaneous” group, has a default value that is the same as the factory map(0.125, 0.1, or 0.09 depending on ECU). Generally, this should not be changed. The “Load DeterminationSmoothing Factor (SD Mode)” has a default value of 1.0. We have found that this works best in most scenarios forSD tuning (i.e. no smoothing for load in SD mode). If, however, you are seeing load changes that are too erratic(or cause a richer than expected tip-in) and cannot be solved by further tuning/smoothing of the VE table, youmay find it useful to lower the SD mode load smoothing factor. Generally, though, it should still be much higherthan the default MAF mode smoothing value.Map Determination Averaging WindowBecause the MAP sensor is one of the crucial inputs to the SD airflow calculation, a collection of factory tablesthat manipulate the final MAP value have been exposed in the software and can be found under the “Sensor Calibrations”group (see table list below):When the MAP delta (current MAP – previous MAP) is within the averaging window of the MAP delta threshold,the ECU will use an average of the last two MAP values as follows:(current MAP+ previous MAP)MAP=2Later ECUs have two separate averaging windows which are used based on an RPM threshold (see table listabove). Earlier ECUs only have a single averaging window (i.e. only a single “MAP Determination Averaging WindowMAP Delta Thresholds” table).Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 23

Generally, these do not need to be modified for SD tuning. However, if you find that MAP is too erratic (and notrepresentative of actual changes in MAP), you may find that expanding the MAP delta range in which the averagingis applied may help. On the other side of the coin, if you find that MAP is not reacting fast enough to actualchanges in MAP, you may find it useful to narrow the MAP delta window.SD Feature ActivationThe SD feature set can be completely deactivated by setting the following table to zero:Disabling the SD feature will cause the ECU to revert back to the OEM logic for determining airflow (based onMAF sensor input). However, this is different from MAF mode in that the SD airflow will no longer be calculatedand the operational mode cannot be changed to SD or Hybrid via a real-time map. SD feature deactivation shouldnot normally be used unless you experience a bug that impacts the safe operation of the SD ECU (although it isrecommended that you switch to the non-SD ECU in this case).Tuning SD – Post-Tune RecommendationsWhen you feel your SD tune is complete, there are several things you should consider in order to maximize thelong-term reliability of the SD tune:• It is important that your reflashed map has the same “SD mode” table value as your real-time tune. For example,if you switch to an SD mode of 1 (i.e. SD airflow) via real-time and tune the car, but do not changethe SD mode from the default of 0 in the reflashed map (i.e. MAF mode), then the ECU will end up switchingto MAF mode the next time the car’s battery is disconnected or the ECU is reset. In addition to the SDmode, it is also important to reflash you final tune to make sure the final tune is always part of the “base”map.• If the SD tune was completed on a dyno, it is important to drive the car under conditions that it is likely tosee during normal operation and verify that the tune is safe and that there are no driveability concerns.• It is highly recommended that a wideband o2 sensor and in-car gauge is installed in the car running SDand that the owner/driver of the car is instructed on how to read the gauge and how to determine what is anormal reading for the tune and given operating conditions.• The owner/driver of the car needs to be instructed about the potential for a heat soaked IAT sensor andunder what conditions this is likely to occur (extended idling, hot soaked re-start, etc). It is important thatthe owner/driver understands that putting the car immediately under heavy load when a heat soaked IATsensor may be a possibility should be avoided when running SD. Instead, under these conditions, allowthe car to get moving without getting heavily into boost for at least a few minutes before putting the car un-Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 24

der heavy load. A wideband o2 sensor with in-car gauge can help here as a heat-soaked IAT sensor willgenerally cause the fuel reading to be leaner than expected.• The owner of the car also needs to understand that practically any engine mod that impacts airflow in anyway may require a re-tune or tweaking of the VE table for cars running SD. This is important as evenseemingly minor mods that a MAF sensor-based tune would have no problem accounting for, might causea significant enough change in VE that there could be fueling and load issues for SD.Tuning SD – Additional TopicsRecommended Calibrations for Aftermarket IAT SensorsWhen an aftermarket IAT sensor is installed, you will need to tune the IAT sensor calibration which will be differentwith an aftermarket sensor as compared to the factory IAT sensor. This is done via the “Intake Temp. Sensor Calibration”table in the “Sensor Calibrations” group.The following shows the recommended IAT scaling for the GM and AEM aftermarket IAT sensors (each screenshotshows one half of the table). Keep in mind that both the axis values (top row) and data values (bottom row)change in this case. Note: These calibrations are provided for your convenience only and do not represent an endorsementfor or against any particular product. Manufacturer’s specifications can change at any time. It is importantthat you verify the sensor calibration you are going to use before tuning SD.Recommended Calibrations for Aftermarket MAP SensorsWhen an aftermarket MAP sensor is installed, you will need to set up the MAP sensor calibration appropriately.This is done via the “MAP Sensor Calibration (Multiplier)” and “MAP Sensor Calibration (Offset)” tables in the“Sensor Calibrations” group. The boost reading (via AccessTUNER software or AccessPORT) should then becompared to an external boost gauge to verify accuracy before tuning SD. The recommended calibrations forsome of the most popular aftermarket MAP sensors are shown below (note: values are shown in psi). Note:These calibrations are provided for your convenience only and do not represent an endorsement for or againstany particular product. Manufacturer’s specifications can change at any time. It is important that you verify thesensor calibration you are going to use before tuning SD.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 25

1. AEM 3.5 bar (Part # 30-2130-50) –> MULTIPLIER = 12.5 psi , OFFSET =-6.25 psi2. AEM 5 bar (Part # 30-2130-75) -> MULTIPLIER = 18.75 psi, OFFSET = -9.375 psi3. GM 3 bar (Part #12223861) -> MULTIPLIER = 8.94 psi, OFFSET = 0.1604 psi4. OmniPower 3 bar (Part #MAP-STI-3BR) -> MULTIPLIER = 9.122 psi, OFFSET = 0.164 psi5. OmniPower 4 bar (Part #MAP-STI-4BR) -> MULTIPLIER = 12.086 psi, OFFSET = 0.169 psiForcing Open Loop FuelingIn some cases, you may find it more straightforward to temporarily force the ECU into full-time open loop fuelingwhen tuning the VE table. This can be accomplished by the following procedure:1. Change the “Primary Open Loop Fueling Min. Activation” table (found under the “Fuel Tables” -> “OpenLoop (Primary)” group) to 14.7:1 AFR (or 1.0 lambda for non-standard units).2. In the “Primary Open Loop Fueling” table(s), change the 14.7:1 AFR cells (or 1.0 lambda cells) to the nextrichest value. For example, change 14.7:1 to 14.59:1 AFR (or 1.0 lambda to 0.99 lambda).3. Change the “Closed to Open Loop Delay” table (found under the “Fuel Tables” -> “Closed/Open LoopTransition” group) to zero. If the ECU in question has multiple cells for this table, make sure every cell iszero.4. Save map and reflash map to car.5. Verify that the ECU remains in open loop full-time by viewing or logging the “Closed/Open Loop Switch”monitor in the AccessTUNER software.It is not recommended that you run full-time open loop operation after the tune is complete. This is because certainscenarios with SD that would result in fueling errors, such as a heat soaked IAT sensor or changes in VE dueto mechanical/aging issues, can be partially mitigated by short-term fueling corrections (and potentially long-termfuel trims) when closed loop operation is active.Long-Term Fuel TrimsYou may find it necessary (or more optimal) to manipulate how the long-term fuel trims are determined when runningSD (and in some cases, for MAF mode as well). The long-term fuel trims are determined based on patternsof short-term correction. They are calculated and applied across four airflow ranges. These ranges are determinedby the “A/F Learning #1” table (under the “Fuel Tables” -> “A/F Learning” group). The following is an example:Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 26

As you can see, there are three values to this table. The airflow ranges are determined from these values as follows(given the example):Range A: 0-

Removing Influence of Rear Oxygen Sensor on FuelingIn addition to the front oxygen sensor, Subarus also employ a rear oxygen sensor in order to monitor the exhauststream after the catalytic converters. When an aftermarket downpipe with high-flow cats (or no cats) is installed,this can change the oxygen content seen by the rear o2 sensor and can cause some undesirable changes toclosed loop fueling. Generally this will result in a richer closed loop fueling target. New tables have been exposedfor the SD ECU that will allow you to mitigate (or eliminate) the effect that the rear o2 sensor has on fueling (offroaduse only). The tables can be found under the “Fuel Tables” -> “Closed Loop Target” group. The following is alist of each table and how to modify them (note: the assortment of tables varies by ECU):• "Closed Loop Fueling Target Compensation (Rear O2) Limits (Max)" – This is the max closed loopfueling target adder based on rear o2 input. The factory default is set to an extreme value so that the limitnever comes into play. However, this can be set to zero to eliminate this compensation on the positiveside.• "Closed Loop Fueling Target Compensation (Rear O2) Limits (Min)" - This is the min closed loop fuelingtarget adder based on rear o2 input. The factory default is set to an extreme value so that the limitnever comes into play. However, this can be set to zero to eliminate this compensation on the negativeside.• "A/F Learning #3 Limits (Max/Min)" - These are the max and min values for the long-term fuel trimbased on rear o2 input. The factory defaults are set to extreme values so that the limits never come intoplay. However, these can be both set to zero to eliminate the influence of the rear o2 based long-term fueltrim."A/F Correction #3 Limits (Max/Min)" – These are max and min values for the short-term fuel trim basedon rear o2 input. The factory defaults are set to extreme values so that the limits never come into play.However, these can be both set to zero to eliminate the influence of the rear o2 based short-term fuel trim."A/F Correction #3 Adder (Increase) A", "...(Increase) B"), "...(Decrease) A", and "...(Decrease) B" –These are the adders to the short-term rear o2 based fueling correction. Setting all four to zero will removethe influence of the rear o2 based short-term fuel trim.Cam Timing (AVCS) Tuning Changes and Effect on VEMost tuning changes are not going to impact VE. For example, once you have your VE table dialed in, you canmake changes to timing, fuel, and boost tuning without needing to revisit the VE table due to those changes.However, there is one exception. That is changes to cam timing (i.e. Subaru’s AVCS). Cam timing changes candefinitely impact VE and will likely require you to tweak the VE table as a result. Because the AVCS table(s) haveload as one of the axes, it may also be useful to keep these tables relatively smooth (i.e. no drastic changesbetween cells). Otherwise, when attempting to dial-in the VE table, large changes in cam timing with smallchanges in load/RPM will change actual VE and you may end up with feedback loop of sorts that makes it moredifficult to tune.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 28

Tuning MAF ModeIn MAF mode (i.e. a value of 0 in the SD mode table), MAF sensor-based tuning is the same with COBB SD ECUas it is with the non-SD ECU. That is, tuning for specific intake hardware is accomplished via the “MAF Calibration”table. The only difference is that the SD ECU will calculate SD airflow (and other SD-related values) whilestill in MAF mode, even though those values are never used in determining airflow. This allow you to, for example,get a starting tune ready for the SD VE table while still running the car in MAF mode.Tuning Hybrid ModeOverviewIn Hybrid mode (i.e. a value of 2 in the SD mode table), you are simply allowing the SD ECU to switch betweenMAF mode and SD mode (and vice versa) based on a series of specific thresholds for MAP, RPM, throttle position(TPS), and MAF voltage (MAFv). In addition, you can also control the behavior of the switching as well as thespeed of the transition.Hybrid Mode - UsesThere are a handful of reasons why hybrid mode might be a better choice than running pure SD mode. The followingare some examples:• If the car runs well on the MAF sensor-based tune but maxes out the MAF sensor on the high end, hybridmode could be used to switch to SD to avoid maxing out the sensor. Running hybrid mode in this casewould reduce the time and effort it would take to get the car to a well-tuned state when compared to a pureSD tune.• If the car has a big MAF set-up and runs well on the high end, but poorly on the low end (i.e. idle/cruise),hybrid mode could be used to run SD on the low end and MAF on the high end to mitigate these issues.This would also reduce the time and effort to finish the car’s tune vs. a pure SD tune.Hybrid Lower/Upper ModeThe first thing to decide is what mode will be used on the lower end and what mode will be used on the upperend. This will be either MAF on the lower end and SD on the upper end or MAF on lower and SD on upper. TheMAP, RPM, throttle and/or MAF voltage thresholds determine the switching from the lower to upper mode (andvice versa). So, for example, if you wanted to switch to SD when one (or more) of these tunable thresholds areexceeded, then you would want SD on the upper end and MAF on the lower end.Whether lower/upper is MAF/SD or SD/MAF is configurable via the following table:If this table’s value is set to 0 (the default value), then MAF mode is used below the threshold(s) and SD mode isused above the threshold(s). If it is 1, then SD mode is used below the threshold(s) and MAF mode above.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 29

Hybrid Threshold Switching BehaviorYou can also decide how the switching from upper to lower (and vice versa) will work based on the thresholds.That is, how many of the thresholds must be exceeded to switch to upper mode and how many values must fallbelow their corresponding thresholds to switch to the lower mode. This is determined by the following table:For example, if this table’s value is 0 (the default value), then the following has to be met to switch modes:• Switch from lower to upper mode: any single value exceeds its corresponding threshold.• Switch from upper to lower mode: all values must fall below their corresponding thresholds (less the correspondinghysteresis)If this table’s value is 1 then the following has to be met:• Switch from lower to upper mode: all values must exceed their corresponding thresholds• Switch from upper to lower mode: any single value falls below its corresponding threshold (less the hysteresis).Hybrid Thresholds OverviewFor the upper mode, a threshold is exceeded if the value in question is greater than the threshold. For the lowermode, the value is considered to have dropped below the threshold if it is less than or equal to the threshold lessits hysteresis (threshold – hysteresis). The threshold table listing is shown below:For example, if your MAFv threshold is set to 3.5v and the MAFv hysteresis is 0.25v, then the threshold is exceededif MAFv is greater than 3.5v and MAFv has dropped below the threshold when MAFv is less than or equalto 3.25 v (3.5v – 0.25v). The reason for the hysteresis is to avoid rapid transitions between MAF and SD modes ifthe value were to hover around the threshold.Hybrid Threshold Individual DeactivationAll four thresholds do not have to play a role in determining the MAF and SD mode transitions. You can removespecific thresholds from the decision process by setting those threshold(s) to unachievable values (which will dependon the threshold switching behavior explained above).Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 30

If the switching behavior is 0 (upper switch = single, lower switch = all), then setting any threshold to an extremelyhigh value that will never be achieved, will remove it from the decision process. For example, you could raise theRPM threshold to an unachievable value of 10000 RPM and RPM would never play a role in the switching.If the threshold switching behavior is 1 (upper switch = all, lower switch = single), then setting any threshold to avalue that will always be exceeded, will remove it from the decision process. For example, you could set the RPMthreshold to 0 RPM and RPM would never play a role in the switching.Hybrid Transition BlendingWhen the decision to switch from MAF to SD mode (or vice versa) is made, the final airflow value will not abruptlyswitch from the airflow calculation of one mode to the other. Instead, over a short period of time, the final airflowwill be calculated as a blend between the on-going airflow calculation in the old mode and the on-going airflowcalculation in the new mode, with the bias increasing from old to new as the ramping process proceeds. This allowsfor a smoother airflow transition between modes (and therefore smoother fueling/timing transition), especiallywhere the SD-based airflow and MAF sensor-based airflow calculations may be somewhat farther apart from oneanother.The ramping is determined by the ramping multiplier. This multiplier (RM below), can range from 0 to 1 and determinesthe blending of the old and new airflow values as follows:Final Airflow=(SD Airflow∗RM )+(MAF∗(1−RM ))In the above equation, if the ramping multiplier is 0, then the final airflow is entirely based on MAF. If is it 1.0, thenthe final airflow is entirely based on SD airflow. Any value in-between is a blend of both MAF and SD airflow withthe bias dependent on the value.When the decision to move from MAF to SD mode is made, the ramping multiplier, which would begin at 0 in thiscase, would be incremented by a specific value (see tables below). The ramping multiplier would continue to beincremented as long as the decision to switch to SD remained and, over a short period of time, the ramping multiplierwould reach 1.0 and SD airflow would entirely be used. The opposite is the case in moving from SD to MAFmode. The ramping multiplier would begin at 1.0 and would be decremented by a specific value as long as the decisionto switch to MAF remained and, over a short period of time, the ramping multiplier would reach 0 and MAFwould entirely be used.The speed at which the ramping process occurs (i.e. the ramping multiplier adder) is dependent on the followingtables:Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 31

As you can see from the tables above, the speed at which the switch occurs can be tuned separately for MAF toSD and SD to MAF. For MAF to SD, higher values in this table increase the speed of the blended transition, whilelower values decrease the speed. For SD to MAF, the opposite is true.Tuning Hybrid Mode – Post-Tune RecommendationsIf the hybrid tune was completed on a dyno, it is important to drive the car under conditions it is likely to see duringnormal operation to verify the safety of the tune and that the hybrid switching occurs as intended. Additionally,for the SD part of the tune, the recommendations outlined in the “Tuning SD –Post-Tune Recommendations” sectionearlier in this document should also be considered.MONITORINGHow to Monitor the TuneIn addition to the monitors already included for the non-SD ECUs, the SD ECUs add additional monitors specificto the COBB SD feature. These will be useful in the tuning process as well as verifying/monitoring the tune once itis complete.SD Mode (Airflow) -> This monitor shows which SD mode is being used to determine the final airflow. This willtell you if SD-based or MAF sensor-based airflow is being used or a blend of both during a hybrid transition. In theAccessTUNER software, this monitor will display/log one of the following strings (AccessPORT value show inbrackets):• “MAF” [0] – Mode is MAF and MAF sensor-based airflow is being used.• “SD” [1] – Mode is SD and SD-based airflow is being used.• “MAF-H” [2] – Mode is hybrid and MAF sensor-based airflow is being used.• “SD-H” [3] – Mode is hybrid and SD-based airflow is being used.• “BLEND” [4] – Mode is hybrid and transition is taking place where SD-based airflow and MAF sensorbasedairflow are blended.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 32

• “MAF-E” OR “ERR” [5 or greater] – An error has occurred and the mode has defaulted to MAF. ContactCOBB customer service if this appears.Mass Airflow (MAF Calibration) -> This is the mass airflow based on the MAF sensor (the output from the “MAFCalibration” table without any limits or compensations applied). This value will always be calculated regardless ofthe current mode. So, you can compare this to the “SD Airflow (Post-Comp)”, which is the final SD airflow, regardlessof whether you are in MAF, SD, or HYBRID mode.SD/MAF Pre-Final Airflow -> This is the final airflow to be used by the ECU (before any factorycompensations/limits are applied). This could be MAF sensor-based airflow, SD-based airflow, or a blend of both(when ramping in hybrid mode). In SD mode, this value will be the same as the “SD Airflow (Post-Comp)” monitor.In MAF mode, this value will be the same as the “Mass Airflow (MAF Calibration)” monitor. When transitioningbetween SD and MAF (or vice versa) in hybrid mode, this value will show the blended value during that transition.SD Airflow (Post-Comp) -> This is the final SD airflow after the IAT, ECT, and barometric compensations (as describedin this document) have been applied to the base SD reference airflow. This value is always calculated regardlessof the current mode.SD Airflow (Pre-Comp) -> This is the SD reference airflow which is calculated based on the ideal gas law usingthe reference temperature of 86 deg. F. That is, this is the SD airflow before the IAT, ECT, and barometric compensationshave been applied. This value is always calculated regardless of the current mode.SD VE (Commanded) -> This is the commanded volumetric efficiency (%) as determined by your “SD VolumetricEfficiency” table. This value is always calculated regardless of the current mode.SD VE Estimated (MAF) -> If the vehicle is still equipped with a MAF sensor that is installed and calibrated correctly,this monitor allows for an estimate of volumetric efficiency based on MAF, MAP, RPM, IAT and the map’s(reflashed) engine displacement value. Keep in mind that specific conditions can skew some of the inputs, resultingin a VE estimate that is not reliable (see “Tuning SD – Starting Values for VE Table” section for details). Thisvalue is always calculated regardless of mode.SD/MAF Hybrid Ratio -> This is the ramping multiplier (RM) which determines the blend of MAF sensor-basedand SD-based airflow when a transition is taking place between modes (when hybrid mode is active). This multiplierdetermines the airflow blend as follows:Final Airflow=(SD Airflow∗RM )+(MAF∗(1−RM ))For example, if the RM is 1.0, then only SD airflow is being used. If it is 0, then only the MAF sensor-based airflowis being used. Any value that falls between 0 and 1 means that a blend of both airflow calculations is being used(as determined by the equation above). This value is only calculated in hybrid mode.SD Hybrid Thresh. Bit Field ->This monitor will indicate which of the hybrid thresholds (RPM, MAP, TPS, MAFv)have been exceeded and which have not. This is useful to verify that the hybrid thresholds you’ve tuned areachieving the desired effect. This value is only calculated in hybrid mode. For the AccessTUNER software, thismonitor will be shown as a series of letters indicating which thresholds have been exceeded as follows:MAF voltage = “V”Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 33

TPS = “T”MAP = “P”RPM = “R”For example, if TPS, RPM, and MAP are exceeded, but MAFv is not, then “TPR” will be displayed. If none of thethresholds are exceeded, then the monitor will be blank.For the AccessPORT, this monitor is displayed as a bit-encoded byte. To determine the thresholds exceeded,you’ll want to first convert the decimal value shown to a binary number. The status of each threshold is given asfollows:(0 = not exceeded, 1 = exceeded)Bit 0 = Mass Airflow VoltageBit 1 = ThrottleBit 2 = Manifold Absolute Pressure (MAP)Bit 3 = RPM(Bit 0 is the last digit in the binary representation of the number, bit 1 is the second to last digit, and so on)For example, a logged value of 9 (binary = 1001), would indicate that RPM and MAF voltage thresholds havebeen exceeded. A value of 0 means none of the thresholds have been exceeded.SD/MAF Load Smoothing Factor ->This is the current load smoothing factor being used by the ECU, which isdependent on the current airflow mode. Details about the load smoothing factor can be found in the “Tuning SD –Miscellaneous Tables” section earlier in this document.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 34

SD REAL-TIMESD Real-Time TuningSome changes were made to real-time tuning for the SD ECUs as compared to the non-SD ECUs:Row/Column Table Data and Dynamic Advance Tables Removed from Real-TimeBecause tuning the volumetric efficiency table in real-time is an enormous benefit and because the space availablefor real-time is limited, the existing real-time set-up had to be modified to accommodate this large table. Allthe real-time tables in the non-SD ECU are carried over to the SD ECU, but the row/column table data (where applicable)is no longer real-time tunable. For example, you will not be able to real-time tune calculated load orRPM for the “Primary Open Loop Fueling” table (i.e. only the fueling targets are real-time tunable whereas theload and RPM axes have to be changed by reflash). This is also the case with any new SD tables (where applicable).Additionally, the “Dynamic Advance” table was also removed from real-time (ignition timing can still be realtimetuned via the “Primary Ignition” table).Other Changes to Real-TimeSome other real-time table changes were made for specific SD ECUs:Dual tip-in enrichment tables were combined into a single real-time table (08-09 WRX)Real-time AVCS table was changed from the “Cruise” to “Accel” version (07 STI)Dual primary fuel tables were combined into a single real-time table (08-11 STI).Real-Time Tunable SD TablesMost of the new tables added for the SD ECU are real-time tunable. See the “Realtime Tables” group in the AccessTUNERsoftware for a complete listing of all real-time tables for a given ECU.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 35

SD MATHSD Airflow MathThis section describes the math behind the COBB SD airflow calculation which is based on the ideal gas law. It isnot necessary to understand this math in order to tune SD, but some may find it interesting.Ideal Gas Law – IntroductionThe ideal gas law is an equation that governs the relationship between the pressure, volume, amount and temperatureof an “ideal” gas:P = PressureV = Volumen = Number of Moles (i.e. amount)R = Gas ConstantT = TemperaturePV =nRTWe want to solve for the amount (n) of gas:n= PVRTOur “ideal” gas is quite simply the air that is being ingested by the engine. For our purposes, we want to know themass of air entering the engine. We can determine the mass of air by using a constant that dictates the mass (ingrams) per mole of air (i.e. the molar mass of air, which we’ll call MMA):Mass of Air (g)=n(moles)∗MMA( g/mole)Because n = PV/RT, we can express this as:Mass of Air( g)=( PVRT )∗MMAIdeal Gas Law – Real-World InputsGiven the above equation, we need input data for pressure (P), volume (V), and temperature (T). Given our enginescenario, these inputs would be determined as follows:Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 36

P = Pressure = Manifold absolute pressure (MAP) as determined by the MAP sensor. Units dependent on gasconstant (R) used (see below)V = Volume = Displacement of the engine (in liters).T = Temperature = Cylinder charge temperature in Kelvin as estimated by the intake air temperature (IAT) sensor.Temperature in Kelvin can be determined as follows: IAT Celsius + 273.15Let’s rename the symbols used for these inputs so they are more appropriate for our engine example:MAP = PDISP = VIAT = TThe constants R and MMA are determined as follows:R = ideal gas constant. Dependent on the MAP units used -> R = 1.205912 (MAP in psi), R = 0.08314472 (MAPin bar), R = 8.314472 (MAP in kPa), R = 62.363669 (MAP in mmHg)MMA = Molar Mass of Air Constant =28.97 g/moleEstimated Mass Air (g )= MAP∗DISP∗MMAR∗IATIdeal Gas Law – Volumetric EfficiencyThe above equation is only valid for our engine example if volumetric efficiency is always 100%, which is obviouslynot the case. We must therefore add VE as a correction factor.Estimated Mass Air (g)= MAP∗VE∗DISP∗MMAR∗IATIdeal Gas Law – Mass AirflowTo determine the air entering the engine per unit of time, we add RPM as an input. Because the crankshaft rotates720 degrees (i.e. two revolutions) for a full stroke, the number of times air is entering the cylinders per second isgiven by:RPM2∗60We combine the above with our mass air equation to get, ultimately, an estimated mass air in grams/second:RPM ∗MAP∗VE∗DISP∗MMAEstimated Mass Airflow (g /sec)=120∗R∗IATCopyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 37

Ideal Gas Law – SD Reference AirflowThe non-linear charge temp correction is inherent to the equation above in determining the estimated airflow.However, it would be useful to be able to tweak the charge temp correction because our IAT sensor input may notalways be exactly representative of actual charge temp. This is highly dependent on the placement of the IATsensor for a given car.To allow for tweaking of the charge temp correction, the SD ECU first calculates a reference SD airflow using aconstant for charge temp (30 deg. C, 86 deg. F). Then the IAT table correction is applied to the reference value.The default values of the IAT table are set-up with the ideal gas law in mind given our reference temperature.Consider the following example:MAP = 1277.359 mmHg (native units of the ECU, which is the same as 24.7psia)RPM = 3000VE = 0.8 (i.e.80%)DISP = 2.5 liters (configurable table value in software)MMA = 28.97 g/molIAT = 303.15 Kelvin constant (our reference temp of 30 C)R = 62.363669 (given the mmHg native ECU units for MAP)For our reference calculation, all the constants can be rolled up into a single constant as follows:constant=MMA120∗R∗IAT28.97constant=120∗62.363669∗303.15 =0.0000127696So, the ECU calculates the reference airflow as follows:Estimated Mass Airflow (g /sec)=RPM ∗VE∗MAP∗DISP∗constantEstimated Mass Airflow (g /sec)=3000∗0.8∗1277.359∗2.5∗0.0000127696=97.87 g/ secSD Final AirflowWe have calculated the SD reference airflow above. However, this airflow is only valid at our given reference tempof 86 degrees F. We must apply the IAT compensation which, with the default values in the tables, follows theideal gas law the same as if we had originally plugged the current IAT value into the estimated mass airflow equationthat was first described in this section. Let’s assume that the current IAT is 122 degrees F. Looking at our IATcompensation table:Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 38

We see that the table calls for -6.19% correction at 122F IAT. We can convert -6.19% to a multiplier of 0.9381((100+x)/100). From our reference airflow example, we calculated a reference airflow of 96.18 g/sec. We applythe IAT correction from our table as follows:SD airflow=SD reference airflow∗IAT correction(multiplier )SD airflow =97.87 g/ sec∗0.9381=91.81 g/ secIf we were to plug in the IAT of 122F (50C) into the original equation given our current example:MAP = 1277.359 mmHg (native units of the ECU, which is 24.7psia)RPM = 3000VE = 0.8 (i.e.80%)DISP = 2.5 liters (configurable by tuner)MMA = 28.97 g/molIAT = 323.15 Kelvin (example IAT of 122F or 50C)R = 62.363669 (given the mmHg native ECU units)RPM ∗MAP∗VE∗DISP∗MMAEstimated Mass Airflow (g /sec)=120∗R∗IATEstimated Mass Airflow (g /sec)= 3000∗1277.359∗0.8∗2.5∗28.97 =91.81g /sec120∗62.363669∗323.15We end up with the same airflow calculation either way, but our “external” IAT compensation table allows us totweak it in cases where the IAT input may not be representative of the actual charge temp.Our final SD airflow is determined after the ECT and barometric compensations have been applied.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 39

Estimated VE CalculationThe SD ECU has the “SD VE Estimated (MAF)” monitor which allows you to determine an estimate of VE if youhave a properly installed, functioning, and calibrated MAF sensor in the car. The math for estimating VE is simplysolving for VE in the estimated mass airflow equation given above. We are using the mass airflow as determinedby the MAF sensor and the “MAF Calibration” table as an input to our estimated VE calculation:MAF∗120∗R∗IATVE=RPM ∗MAP∗DISP∗MMALet’s take the previous example and solve for VE given our previous estimated MAF of 91.81 g/sec:VE= 91.81∗120∗62.363669∗323.15 =0.80(or 80%)3000∗1277.359∗2.5∗28.97As you can see, we end up with the same VE calculation as used in the original estimated mass airflow example.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 40

APPENDIXAppendix – Aftermarket IAT Sensor InstallThe following describes how to install an aftermarket intake air temp (IAT) sensor by modifying the factory wiringharness. This information is applicable to the 2002-2012 WRX and 2004-2012 STi:• Locate and unplug your factory MAF sensor wiring harness.• For GD Subarus (2002-2007 WRX and 2004-2007 STi), cut the Brown and Green/Red wires of the factorywiring harness so that you have a suitable length.• For GR Subarus (2008-2012 WRX and STi), cut the Yellow/Red and Yellow/Blue wires of the factory wiringharness so that you have a suitable length.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 41

• Strip and solder together the two wires of the aftermarket IAT sensor pigtail and the engine wiring harness.• Plug the MAF sensor harness back in (if MAF sensor is not being removed).• Modify the “Intake Temp. Sensor Calibration” table in the AccessTUNER software (under “Sensor Calibrations”group) so that the appropriate calibration is achieved for your aftermarket IAT sensor. Note: Recommendedcalibrations for some aftermarket IAT sensors can be found in the “Tuning SD – Additional Topics”section earlier in this document.• Save your map and reflash to car.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 42

• Before tuning, verify that the new IAT sensor is reading properly by monitoring Intake Temp via the AccessTUNERsoftware or the AccessPORT.Copyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 43