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Planning & Plotting a YJ Wrangler Repower: So Many Options, Only One Engine

Posted in Project Vehicles on January 31, 2019
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Every now and then a vehicle transcends the boundary between simple transportation device and valued family member. That’s what happened with my 1989 Wrangler, Project Why-J. I originally bought it back in September 2008 for a paltry $500. The clutch master cylinder needed to be bled and refilled, and it needed a battery; otherwise I put the little Jeep into daily service. As the technical editor of Jp magazine at the time, I covered a series of mild modifications ranging from upgrading the factory axles with 30-spline alloy axleshaft, Eaton E-Lockers, and 4.88s, to a 2 1/2-inch Rubicon Express suspension, upgrading the NP231 to 3/4-ton specs with internals from JB Conversions (, and swapping in an AX15 transmission with the help of an Advance Adapters kit ( There were obviously more stories I did with this Jeep over the ensuing 11 years I’ve owned it, so search for “Project Why-J” for more stuff like the GenRight rollcage (, Bestop interior (, and much more.

But throughout all the modifications one thing has remained more or less constant: the factory 2.5L TBI engine. With about 250,000 miles the engine is by now really, really tired and has begun suffering from hard-start and stalling issues. I could rebuild it and go through the various injection components, but I think it’s time for a repower. The AX15 transmission will be great for anything from an LS swap to a Cummins R2.8 repower to … oh, I don’t know. I’ve come to enjoy the limited power output of the 2.5L. It has forced me to slow down and smell the roses. Heck, this Jeep doesn’t even have power steering. I don’t need 1,000 hp, so I’ve got my engine swaption choices narrowed down to three: either a Cummins R2.8 crate engine, a TDI turbodiesel out of a wrecked VW, or the old 3.9L all-aluminum Range Rover V-8 that came out of Tech Editor Verne Simons’ Derange Rover UA2018 project build. Otherwise the Jeep will only require a few minor refreshers, which you can read about in the captions.

With no A/C, power steering, or other options, the factory engine bay is uncluttered, if nothing else. The factory 2.5L TBI engine is dog-tired and ready for retirement. I’m considering a couple diesel options, but just might go grab the 3.9L Rover V-8 from Verne Simons’ Derange Rover project. I’d ditch the factory Rover injection, add an Edelbrock Buick 215 four-barrel intake, top it with a self-learning aftermarket TBI system, and enjoy the lightweight gas eight-popper.
At one point I was considering building a ludicrous supercharged stroker LS3 engine for this thing, so I built up the NP231 with 3/4-ton parts from JB Conversions and swapped in an AX15 transmission that I hoped I could sort of keep alive behind a powerplant like that. Thankfully I never stuffed a 790hp engine in Why-J because if I had, I probably would’ve wrapped the vehicle around a telephone pole by now.
Back in the day I had my buddy Jay Miller install a now-discontinued Superior Super 30 and Super 35 kit with 4.88 gears and Eaton E-Lockers in the factory axlehousings. The kits replaced the factory axleshafts with high-quality 30-spline alloy units, and the front employs a special seal and one-piece shaft that omits the factory Central Axle Disconnect system. Unfortunately the front axle seals began weeping a few years ago, so I’ll need to yank apart the front axle and toss in some fresh seals.
While I love the simple leaf-spring suspension, I’ve never really been a fan of the standard shackle-forward arrangement in the front suspension. I’ve contemplated doing a shackle reversal from time to time, but nowadays I’m thinking I may link the front suspension to push the axle forward a bit. I dunno. Or just a shackle reversal. It’ll be one or the other. We’ll see.
I installed the weld-together GenRight rollcage system and added the Spiderweb shade top years ago, and it has been one of the most enjoyable upgrades I’ve done. The GenRight ’cage is much safer, and the Spiderweb shade allows the windshield to easily be folded down and doesn’t flap in the breeze, unlike a standard bikini top attached to the windshield channel. I gave up running a real soft top on this Jeep years ago.
The Why-J has been an exercise in moderation. I’ve resisted the urge for huge lift height, gargantuan tires, and other excessive upgrades. However, I did recently up the tire size from 31s to the 32x11.50R15 BFGoodrich M/T KM3s that I’m currently testing for our June 2019 special wheel and tire issue. Will I ever do 33s or 35s? Probably not. Wheeling a weenie Wrangler is just too much fun.

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