Jeep Engines - Oljeep

4.0L POWER TECH IN-LINE 6 (CYLINDER HEAD) 163The most popular performance aspect of cylinder heads isair flow or cfm. Although you should consider both intakeand exhaust flow when evaluating a head, only the intaketends to be considered by most racers. Additionally, midliftflow and “area under the curve” numbers are moreimportant than the peak flow number, although peak flow isthe “popular” number. (Refer to Evaluating Cylinder HeadAir Flow, later in this section, for more information.)Valve gear is a very complicated area. You must havesomething that works. Since it must work with the head andthe block that you are using, you must consider it. Headscan be very expensive. If you are building a new engine,you can get any system you want, it just costs money. Butif you have a valve gear system already that you want touse, or you have an existing engine that you want to installthe head on to, then you should consider the valve gear.New valve gear could cost as little as a few hundred dollarsor as high as $2,500 (or more). Although the valve gear forcast iron heads tends to be the most readily available andthe least expensive, there may be aluminum heads alsoavailable that can use all or some of the same hardware.Intake manifolds can also be very expensive. Big intakestake big intake manifolds. Exhaust port flanges may change.Standard production intake/exhaust gaskets (P4529243) arereadily available from Mopar, or easily modified fromexisting parts. If a special gasket is required and it is onlyavailable from one, non-Mopar source, be careful.Although the valve cover is not changed very often(because of the added expense and complexity), there arecases where the valve cover shape was changed and the oldcover will NOT fit on a new head. Be sure to check this outbefore you buy!Cylinder head attaching hardware is rarely changed. However,in some cases the head bolts may have been changed. Find outbefore you buy-this can be a hidden expense.The cylinder head must get oil under pressure. Some casesrequire external oiling. Oil returns are never talked aboutbut are necessary. Drag racers don’t usually consider oilreturns, but they should.An aluminum head is about 20 pounds lighter than a typicalcast iron head. Most cast iron heads for a given engineweigh the same. A heavier cast iron head would certainlynot be desired. Some aluminum heads may only be five toten pounds lighter than a production cast iron head, but thisis usually caused by added “features.”Finally, we have the camshaft. You might ask what thecamshaft has to do with the cylinder head. The camshaftdetermines how much lift you are going to use. If you use.600” or less, then you don’t want big port windows andextra big valves. If the vehicle is heavy, you also DO NOTwant big ports and big valves. If you have largedisplacements, then you almost have to have large ports andbig valves. There are solutions to some of these problems,but they cost more money.What does all this mean? If you make the material choicefirst (aluminum or cast iron) then consider pistons andcamshaft lift, the decision is made by adding up the costs.Refer the total cost back to your priorities list and youshould have the best answer for you and your race vehicle.There are so many ways to get high flow today that youcannot consider air flow only and expect to choose the righthead. As more heads come on to the market and more featuresare added to each version, this process will becomeeven more important.CYLINDER HEAD REMOVAL AND INSTALLATIONPROCEDURESRemovalThe following procedure can be performed with the enginein or out of the vehicle.Warning! DO NOT remove the cylinder block drain plugsor loosen the radiator draincock with the system hot andpressurized because serious burns from the coolant canoccur.1. Drain the coolant and disconnect the hoses at thethermostat housing. DO NOT waste reusable coolant.If the solution is clean and is being drained only toservice the engine or cooling system, drain the coolantinto a clean container for reuse.2. Remove the air cleaner.3. Remove the fuel pipe and vacuum advance hose.4. Remove the cylinder head cover. Refer to CylinderHead Cover Removal, in this section for the procedure.5. Remove the capscrews, bridge and pivot assembliesand rocker arms. Alternately loosen each capscrew oneturn at a time to avoid damaging the bridge.6. Remove the pushrods. Retain the pushrods, bridges,pivots and rocker arms in the same order as removed tofacilitate installation in their original locations.7. Loosen the alternator drive belt and remove thealternator bracket-to-cylinder head mounting bolt. Theserpentine drive belt tension is released by looseningthe alternator.8. Disconnect the power steering pump bracket. Set thepump and bracket aside. DO NOT disconnect the hoses.