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1991 Jeep Wrangler YJ Buildup - Project Old School

Phil Howell | Writer
Posted May 17, 2007

Part II: Continuing The Build

We had a person ask us, "What's 'old school' about building a Jeep with just about every part being new or high-tech?"

If this person had read the first installment a little more carefully, we named this project as we did because we're building it in a neighbor's garage as we used to in the old days, and we're keeping the leaf springs under the axle, just like the old days. This person also commented that our neighbor had all the tools and equipment of a high-end fabrication shop. Wow! Did you know that you too can have a high-end fabrication shop if you own a torch, a small MIG welder, and a set of tools? We're glad, though, that people are reading and making comments, whether positive or negative.

Our '91 Jeep YJ Wrangler sat idle for a time while we resolved some transmission issues. We told you in our first installment that we planned on mating a GM 4L60E automatic behind the Hemi, via an Advance Adapters adapter. Our prototype adapter needed some modification, so we had to go in another direction in order to get our project finished in a timely manner. That direction was trading our Advance Adapters 4L60E for an Advance Adapters 727 TorqueFlite automatic. According to everything we had heard, the 727 would bolt right up to the Hemi with no adapter necessary. In fact, the sales brochure for the stand-alone MPI 5.7 Hemi says you can bolt it right in to your older Challenger, Road Runner, etc., that had a small-block A-pattern block in them. Yes, the bolt patterns match. No, it's not that easy.

Most of the older Mopar engines were externally balanced. The new Hemi is internally balanced, so it requires a zero- or neutral-balance torque converter and flexplate. Also, the older torque converters had an asymmetrical bolt pattern, so they won't bolt up to the Hemi's symmetrical, 90-degree-bolt-pattern flexplate. No problem, just use an older Mopar flexplate. You know the one, it looks like a cross. Oops, the small-block flexplate fits a six-bolt pattern on the crank and the Hemi is an eight-bolt pattern. Still no problem, right? The old Mopar big-block Hemi and 440 Six-Pack had an eight-bolt pattern and we can use one of those flexplates. Nope, wrong again. The new Hemi's eight-bolt pattern doesn't match the old pattern. Mopar says in its instructions to use the flexplate and converter from a new Ram pickup. Right. The new Ram converter has a computer-controlled lockup. The whole reason to use the stand-alone Hemi is to install it in older vehicles that aren't computer-controlled. The new Hemi has no transmission programming in its small brain, and our old Jeep (or Challenger, Road Runner, etc.) has no computer to control the transmission and torque converter.


Currie Enterprises
Pro Comp Suspension
Chula Vista , CA 91914
Master Power Brakes
Mooresville, NC 28117
Precision Gear
Suwanee, GA 30024
Advance Adapters
Paso Robles, CA 93446
Walker Evans Racing
Riverside, CA 92516
4 Wheel Drive Hardware
wef, AK
PSC Motorsports
Azle, TX 76020
HM Engineering
Fountain Valley, CA 92708
Deaver Spring
Santa Ana, CA 92701
Tuffy Security Products
Eaton/Detroit Locker
Gen-Right Off Road
OMF Performance Products
Don's Professional Collision Repair
Millville, UT
Mountain Off-Road Ent. (MORE)
West Motor Co
Preston, ID
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