From Junker to Stroker

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By Dino Savva

The 4.0L High Output engine in my 1992 Jeep Cherokee Laredo produced an estimated 193hp @ 4750rpm & 239lbft @ 3500rpm in standard form. Maxed out with external bolt-on performance modifications, a ported/milled cylinder head, and with the compression ratio raised to 9.07:1, outputs increased to an estimated 235hp @ 5100rpm & 269lbft @ 3800rpm. The details are on Dino's Jeep 4.0 Performance Site. For most people, that would be more than enough power to motivate a vehicle weighing only 3607lb (1636kg) including driver but I got used to the performance (1/4 mile in 15.39 @ 91.1) and I craved for more. Since I wanted to keep the engine naturally aspirated, my routes towards more HP/TQ were as follows:

1) Internally modify my existing 4.0 engine.

The engine ran perfectly, was leak-free, and oil consumption was negligible, but it had done 174,000 miles. If I was going to internally modify it for more performance, I'd realistically need to plan a full rebuild as well. To upgrade performance, I'd swap in a Crane 260/272 degree CRN-753905 performance camshaft and mill 0.020" from the block deck to raise the compression ratio to 9.5:1. Unfortunately the engine would still have the same displacement and HP/TQ gains would not be enough to justify tearing a strong-running engine apart so I ruled out this option.

2) Swap in a larger displacement V8 engine.

I love the sound and performance of a V8 but swapping one into my Jeep would have been a very expensive exercise. Custom parts and a lot of fabrication are needed to get it set up properly. The Jeep would have been out of action for too long and since it's my daily driver, I ruled out this option as well.

3) Swap in an off-the-shelf stroker long block engine.

There's a choice of displacements from 4.6 to 5.0L. That would have been much easier and less time-consuming to do than a V8 swap, and the engine would have come with a warranty. The only downside was the high cost of buying the engine (the cheapest were 3300USD from Golen Engine Service and Custom Design Performance) and shipping it to Saudi Arabia, so that wasn't a viable option for me either.

4) Build a 4.6L stroker engine based on a junkyard 4.0.

The appeal of this route was that I could keep my existing 4.0 going, build the stroker in my spare time, and drop it into my Jeep whenever I wanted to. It would cost much less than 3300USD to build and I'd also gain an intimate knowledge of the engine as I built it up. I could then sell my old 4.0 engine once the stroker was up and running to recoup some of the cost of the stroker build-up. The stroker engine looks exactly the same as the 4.0 externally so it's a straightforward engine swap. All the existing ancillary components bolt up to the stroker without modification, making this a clean installation. The bolt-on performance modifications that I already had on my Jeep were also compatible with a stroker so the choice of the home-built stroker route to more performance was, for me, a no brainer.

The next question was whether to buy a complete stroker kit or assemble one of my own. At the time (February 2005) Hesco, Accurate Power, Speedomotive, and RPM Machine supplied stroker kits for the 4.0. A basic stroker kit will consist of a stroker crankshaft, rods, rod bolts, pistons, piston rings, and rod/main bearings. Some kits also include a performance camshaft & lifter kit. I shopped around and bought each of these components individually, saving a lot of money compared to buying a complete stroker kit.

Reground (-0.020" rod, -0.030" main) AMC 258 crankshaft 3214723 with Clevite 77 rod & main bearings from Atlanta Crankshaft Exchange.

Reconditioned AMC 258 connecting rods (707 casting) from e-bay. These have been magnafluxed, shotpeened, resized, and are weight-matched to within 1g. Weights are 695-696g with rod bolts.

Sealed Power 677P pistons. These are weight-matched and each weighs 735g with pin.