We slammed the 4.7L inline-six stroker engine from Mopar Performance in our ’91 Comanche in a weekend (“Weekend Mopar 4.7L Stroker,” July ’11) and have been enjoying it ever since. Just enough time has passed since daily-driving our last 258ci-powered Jeep that we forgot what that low-end grunt was like. Once we got through the break-in period and stomped on the gas we got a very pleasant reminder. For those of you that don’t know, this stroker engine is basically a 4.0L block and HO head with a 4.2L (258ci) crank adapted to it. The stroker provides the high-end power and drivability of the 4.0L with the low-end grunt and locomotive-like pulling power of the 4.2L. It’s the best of both worlds.
Since we first scrambled to get the engine in the truck, we’ve converted it to four-wheel drive, taken it to Moab for Easter Jeep Safari and wheeled it for more than a week, and made it back home without a hitch. Over the past few months, we’ve racked up over 5,000 miles on the new stroker, kept lots of records, had a few problems, and came up with a few solutions. This is the second part of our three-part series with this engine. In the next part, we will throw all the usual power adders at the engine to see how it responds.
There are a lot of guys out there that have complained of problems with the way the factory computer deals with the larger-displacement engine. To date, we’ve had no problems at all once the factory computer “learned” the new engine, and that is one of the reasons for pumping up the power in the next installment. Will the factory computer ever hit a wall like so many say? Or will we be able to make the engine not only run, but make more power through simple modifications? Only time will tell, but for now, here are our experiences with the 4.7L engine in our Jeep.