Merlins Ralliart and EvoX TUNING GUIDE Version K.pdf - EvoScan

MERLINS RALLIART & EVOLUTION-X TUNING GUIDESECTION 6 – IGNITION TUNING PART 2 - KNOCK TUNING6.01-KNOCK TUNING - KNOCKSUM & OCTANE NUMBERKNOCKSUM and OCTANE NUMBER are the parameters which combine to give thefinal ignition timing value, operating temperature corrections aside.KNOCKSUM is generated by the ECU, from the input from the knock sensor and ithas several tables and variables that can be manipulated to subtly alter the finalKNOCKSUM result. This has particular relevance to the tuning fraternity, as someengines exhibit what has been described as “phantom” or “false” knock. Thisbecomes even more important when engine internals, like forged pistons, areadded to the equation. It has been reported that some aftermarket clutches canhave an effect on false knock as well as general engine aging.OCTANE NUMBER controls the interpolation between the HI-OCTANE and LO-OCTANE fuel and ignition maps and is a dynamic number stored in the ECU randomaccess memory (RAM). The OCTANE NUMBER starts off at a value of hex 255, for100%. HI-OCTANE map operation. The maximum value is not quite an arbitrarynumber, as its value would have an affect on the driving time it would take totransit from fully Hi to fully LO-OCTANE map operation for a given rate of knock.The following equation describes the method for deriving the new ignition timingfrom the two timing maps:(((255 -octane#) x LO-MAP) + (octane# x HI-MAP)) ÷ 255Using a LO-MAP value of 10° and a HI-MAP value of 20°, with an octane number of128 will yield a ignition timing value of 15, a 50% shift. With the same map values,and an octane number of 250, ie 5 counts have been deducted, this yields anignition timing value of 19.8°. Only a 2% shift, so the shift from the HI-MAP to theLO-MAP is gradual.OCTANE NUMER is decremented y 100/255 = 0.39216. This can readily beobserved from EvoScan log files.If the KNOCKSUM is 6 or higher, then the OCTANE NUMBER in the ECU’s RAM willbe decreased by 1 on a timer.If the KNOCKSUM is 3 - 5 then the OCTANE NUMBER is not changed.If the KNOCKSUM falls to 0 - 2, then the OCTANE NUMBER will be increased by 1 ona timer. However, OCTANE NUMBER will not increment until the engine coolanttemperature is above a preset value.REV: 0.K merlin@three.com.au Page 53 of 134