Jeep Engines - Oljeep

232 MOPAR PERFORMANCE PARTSf. Ignition Timing (if adjustable)Ignition timing or spark advance is very importantto fuel economy. It is very important that it be setcorrectly. Most late model vehicles have a tag inthe engine compartment that provides the correctspark advance setting for that vehicle’s engine.This initial timing should be set at the specifiedidle speed and with the vacuum advance hosedisconnected. In the interest of fuel economy, youshould always run the maximum allowable sparkadvance.g. Lipht Engine OilsRunning a light engine oil will also help fueleconomy. Caution must be used with light oil as itmay not lubricate the engine properly under highload or temperature conditions. It is mostimportant that a multi-viscosity, high quality oil beused. Avoid aftermarket additive “viscosityimprovers” and heavy oils such as SAE 40W or50W. Engine oils lighter than SAE 10W30 are notgenerally recommended for six cylinder cast ironengines. If in doubt, check your owners or servicemanual.2. Rework (Simple Modifications)With the basic tune-up and check-out operationsperformed, we have a solid foundation for makingfurther improvements. These improvements requirespecial parts but offer further fuel economy gains overthe best stock package. Since these changes do use newand different parts, be sure to check your warranty andlocal track regulations BEFORE you make any change.3. Rebuild (Major Modifications)With all the easy to reach items completed, furtherimprovements can be obtained by more extensivemodifications, which will require greater time and effort.These modifications require removing the cylinder headand/or intake manifold. If you do your own work, thecost of these modifications is relatively low.a. Blueprint Compression RatioBlueprinting the engine compression ratio willprovide an increase in fuel economy. To blueprintthe compression ratio, the cylinder head must beremoved and milled at a machine shop. After thehead is removed from the engine, clean it andvolume check combustion chamber volumes.b. Valve JobA good valve job is very important to fueleconomy. The valve job and cylinder head millingshould be done at the same time for simplicity andto reduce cost. The head will have to be taken to amachine shop or valve grinder to have the valvesground, providing the best possible cylindersealing. Any valve in poor condition should bereplaced. Always reassemble the head with newvalve stem seals.c. CamshaftChanging camshafts rarely improves fueleconomy. If a high performance camshaft has beeninstalled in the engine, better fuel economy maybe obtained by using the standard productioncamshaft that came with the engine. Since mostproduction engines are built with mild camshafts,there is very little, if any, fuel economy advantagein replacing the production camshaft.ChassisIn general, when trying to compare camshaftsfrom different sources, cam lift is the mostvaluable piece of information. More lift, moreperformance (horsepower); less lift, lessperformance (but more fuel economy). For moreinformation, refer to ‘Camshaft and Valve Gear’section of this chapter.With the engine adjustments and modifications covered, wecan turn our attention to the rest of the vehicle.Tire PressureThe air pressure in a tire affects fuel economy.Generally, higher tire pressures will provide better fueleconomy by reducing the tire’s rolling resistance.Fluid LevelsOperating the transmission and rear axle at less thantheir “full” fluid capacity will help fuel economy. Anautomatic transmission can be run one pint below fullwhile a manual transmission and rear axle can be run a1/2 pint below full. Caution must be used. Loweringfluid levels below these recommendations may causetransmission or axle damage.Front End AlignmentHaving the vehicle’s front end aligned properly willprovide improved fuel economy and reduced tire wear.The vehicle’s front end toe-idtoe-out condition has thegreatest effect on fuel economy. It is important that thetires point straight ahead when the vehicle is travelingin a straight line. Stock caster and camber settingsshould also be used.. ..._