How to Not Dominate the World With Lots of New Horsepower.

Our faithful and much loved #430 Jeep Cherokee road race car has exceeded pretty much everybody’s expectations, recently being named by Car and Driver as the Greatest Road Racing Cherokee in (LeMons) History. The “in LeMons” caveat was quickly redacted by The 24 Hours of LeMons themselves, meaning we have a lot to live up to. But how do we crack through that glass ceiling that exists for 2WD SUV road race cars? A question that is commonly asked by nobody, anywhere.

We’ve been competing with basically a stock 4.0 for years, and have had a love/hate relationship with it. On one hand, it has six pistons in a straight line, as god intended. The AMC Six is typically reliable despite abuse and neglect, and usually good for 300k miles, but ignore what the Internet tells you; you just can’t make significant horsepower out of them on a LeMons budget (which is to say, basically nothing). We dabbled with the idea of forced induction, but that brought up questions of reliability (which we had *just* conquered) or a stroker 258/242 hybrid which would blow our budget and are fickle by nature. We knew the Jeep had the awesome Falken tires and the brakes to compete with the big dogs, just not the horsepower. The Cherokee’s barn-door-inspired aerodynamics were no help over 50 mph, either, further highlighting the lack of brute power.


So, what to do? It is commonly accepted that the least reliable engine in all of LeMons history is the normally bullet-proof 350ci Small Block Chevy V8 family of engines. So obviously we decided to pursue that route. Actually swapping in a SBC motor is not at all new in the Cherokee world, and the entire time we’d been screwing around with the AMC/Chrysler 4-litre engine, there was this Chevy V8 sitting in the Petty Cash High Technology Centre and Proving Grounds’ shop that had been scavenged and ear-marked for another project. It came from a wrecked ’99 Silverado pick-up that we’d bought and parted out years ago for said other project. The parting out and scrap value of the truck we bought put the last remaining component, the 5.3 liter LM7 V8, at an actual cost to us of about $150…well within our LeMons budget.

Stats for the Silverado truck motor looked encouraging, 270 bhp and 315 lb/ft out of the box compared with 173 hp/220 lb/ft for the AMC 6 cylinder. Also, mated to the power hog of an automatic transmission that we were saddled with in order to stay within our budget, we never saw anything like the advertised hp out of the AMC Six.

Conventional wisdom when doing a Chevy V8 swap is you just toss in the GM transmission that was originally behind the V8. But no, that would be too easy and would blow our $500 budget. Besides, the Aisin-Warner AW4 auto had been supremely reliable, despite an inadvertent 85 mph shift past OD into reverse one time. We also got in touch with some Toyota Supra experts, a car which inexplicably shares basically the same transmission. We mailed Fringe XVO our valve body and they sent us one back that had been tweaked for faster shifts; counter intuitively this actually reduces wear and keeps heat in check. With this mod and a couple coffee table sized trans coolers, we stuck with our trusty slush-o-matic and made an adapter to make it bolt up to the Gen III Chevy V8…how hard could it be? Turns out the answer is “very.”



In the end we used a 4L60E bellhousing from a Chevy Astro, a flex plate from a Camaro with spacers welded to it then bolted to the flex plate from a Cherokee, bolted to a Cherokee torque converter, all held together with an adapter plate that we made with a drill press, band saw and the power of positive thinking. We spent a great deal of time getting this bastardized combination to “kinda-sorta” work. Niggling details and lingering doubts left us with no time to do any real testing of the combination before race day. Knowing that we were venturing into the unknown, we ponied up for a fancy-pants, track-facing paddock/garage rental at Sears Point/Infineon/Race Sonoma/whateverthehell they’re calling it now. Baller status for sure.


We spent so much time fiddling with the transmission adapter (literally over night, through the morning, right up until the green flag dropped) that we neglected to give our new motor much attention. Before even dropping the 5.3 into the Jeep, we’d pulled the oil pan, checked the bearings, compression in all the cylinders, etc and everything looked hunkey-dory. It made great oil pressure (40 lbs at idle when hot) and after a few spirited excursions around the paddock we were fairly confident that this crazy idea would work. We even used a Camaro/Firebird LS1 oil pan with lots of baffling, our Accusump from the 4-litre and AmsOil 20/50 race oil from We finally had the winning combination after 12 races: It was our race to lose.

Here’s our first lap out:

With our uber-conservative exhaust and only one lap to prod the limits, things didn’t really feel all that much faster than before. Hmphf.

After coming into check why the oil pressure was dropping off, the motor seemed to heal itself and regain its previous strong pressure. Faulty gauge? Ghost in the machine? Meh. Back out we went, with all the bugs surely sorted. Ha.

This time it was something stupid on our part, a coolant line that needed to go to the overflow tank and not be plugged with a screw like it was. So once more back in we came for a quick fix; by this time any hope of a class win was gone. You just can’t spend that much time in the pits and have any chance in the hyper competitive California races with 175 other race cars. So with a more relaxed pace we went back out…and had the same mysterious loss of oil pressure after 2 laps. Okay, fine..we’ll do it right and try to get the car back on track, but do it with an eye on actually fixing the problem, not just a slapped together short term solution. We decided to pull the oil pan and check the oil pick-up to see if it might be clogged.


It was…a lot. And there was also a great deal of metallic debris that looked remarkably like the bearings were tearing themselves apart. In 5 laps.


Hey, no biggie…we’ve swapped an engine every time we’ve raced at Sears Point, just never this early on. Par for the course, Semper Gumby and all that. The local generic parts store had rod bearings in stock for a 5.3 V8 (no surprise, GM has been churning them out by the millions for nigh on 15 years) for almost free. We decided that in addition to cleaning out the oil pick-up we’d throw in some new bearings for added insurance. With a couple hours to spare in Saturday’s session, the Jeep made a triumphant return to the track.


For two laps, then good bye oil pressure. We were officially flummoxed and out of ideas. Back into the engine we tore. We called LSx experts. We went from team to team to see if they’d ever heard of anything like this. We called Miss Cleo the Psychic. No help. In the end we put everything back together and changed the oil again, with a fresh filter hoping we might be able to get rid of the sludge that was giving us so much grief. Nope.

With no time left to source a junkyard motor at a reasonable price, we decided to pack it in, start drinking and save what was left of the motor and at least take the checkered flag.


Not a totally hollow victory, but also not very satisfying considering the staggering number of hours we’d spent in the shop putting the puzzle together. There is one ray of sunshine, a silver lining of sorts: The basic concept of a much more powerful motor in the old XJ chassis actually felt pretty composed and controllable. Of all things, the one-off trans adapter seems to work, and the tranny itself appears to be up to the task. There are some things to be addressed and sorted, but as a testing/proof of concept the weekend was a success, albeit a very expensive one. But hey, that’s racing and we had to pay the piper eventually. Hopefully this means our next event (Buttonwillow Raceway Park, June 29-30) will be trouble free. Hey, we can dream, can’t we?

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4 Responses to How to Not Dominate the World With Lots of New Horsepower.

  1. Sabrina Hill says:

    Best of racing luck to you, I’m having fun going fast, and turning left with a V-8 powered Mustang 2 here.

  2. Greg B says:

    Are you still running the stock vibration damper? Sounds like you’re getting some kind of torsional vibration or changing the load on the crank shaft that might be wiping the bearings early. Is it all bearings or just front or rear? Is your welded flex plate still pretty true or did the welding warp it? Maybe out of balance as well? Good luck, love your race SUV!

    • The issue wasn’t bearings, we replaced them just as a band aid/Hail Mary that might let us limp through the rest of the race. There wasn’t significant wear on them. Pretty sure imbalance isn’t this issue.

  3. Andrewr05 says:

    I still can’t believe that AW4 takes all this abuse. I realize you aren’t pumping a shit load of power through it, but to be power shifting that automatic like a manual all day on a track and to have it stay in one piece is pretty amazing.

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