Building a Jeep 4.0L Stroker
Introduction
By Robert W. Bryce
The Jeep 4.0L I-6, introduced in 1987, has received many praises over the years. And virtually every Jeep owner will surely agree with them. It produces very good torque, power, and throttle response from idle right to the red-line. However, this doesn't mean that some Jeep owners still feel that there is something, well, lacking, especially if the engine is getting a little long in the tooth. There are a few options for late-model Jeep owners; these tend to follow the old adage that "there is no substitute for cubes".
One option is to swap in an entirely different engine. There are kits available to swap in most all of the popular V-8's. However, this is not a viable option for many people since many unexpected gremlins often rear their ugly heads during these swaps. These can range from cooling, to electronics, to exhaust routing, to even oil-pan clearance. Locating the appropriate adapter to mate the engine to the transmission is usually the easy part!
A second option is to build the 4.0L to produce more power. There are many options (even superchargers and turbochargers) available for this motor, and at least two companies sell stroker kits. Stroking is appealing since the power band can remain relatively low while increasing overall torque, especially if a rebuild is in order anyway. However, the price tags on these kits will make all but a very few bank accounts whimper! The following article overviews a project to build a stroker engine out of the Jeep 4.0L, but without going hungry for a few months.
The 4.0L comes in 3 different flavors, the early (pre '91) era 4.0L, the 4.0L HO version, and the current version found in the TJ. For the HO version, the factory updated the design of the intake, cylinder head, camshaft, exhaust, and EFI. The release of the TJ saw more improvements to the 4.0L, but these engines are still relatively scarce and expensive in wreckers. A great deal was found on a very fresh '93 4.0L, which was used for the core of this project. Any 4.0L block would work, though.
Before we dive into the project, I should state my goals. We are not going to try to build a high-horsepower engine. What we are looking for is a good, reliable stock replacement motor that has more low-end torque, and is equally ideal for the trail, the street, and cruising on the highway. The more low-end grunt the better. It will replace a 4.0L in an '89 Jeep Comanche which has 280,000km on the odometer.
Thank You's
Before I get into the details of the project, I must first mention that there are many people I must thank for the help and the advice and the knowledge that they contributed to this project. Without their contributions, I may not have started or completed such an undertaking. I won't claim to remember to mention everyone but the most influential people in this project are (in alphabetical order):
Rick and Alan verifying correct crankshaft end-play.
Yeah, right.
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Wayne (Fozzy) Foster
Joe Hinson
Andy James
Dave Kamp
Richard (Tiny) Reimer
Jeff (Jefe) Reynolds
Ed Stevens
