Part 1: Junkyard Jeep Powerplants
I had just completed an AX15 swap behind the 2.5L in my ’89 Wrangler. And wouldn’t you know it, shortly afterwards the engine started getting tired and developed sporadic drivability issues that made me question its reliability on any drive more than 20 miles from home. So, rather than rebuilding my stock 117hp, 135lb-ft TBI four-banger, I began searching for a replacement engine to swap in its place. In my opinion, a V-6 or I-6 conversion is just too much work for the power and drivability gains they offer, so I immediately started searching for a complete, running V-8 donor vehicle from which I could yank everything I’d need: engine, fuel system, accessories, exhaust, and sensors. I also searched for complete take-out engines, but was surprised at some of the prices being asked. Still, I soldiered on.
At first, I thought I wanted a dirt-simple TBI Chevy 350. I gave myself a max budget under $1,000 to score my new powerplant (not including adapters or swap components), but you know how things go. First, all of the donor vehicles I found in my price range were either beat to death or had over 200,000 miles on themand all of the take-out engines looked suspect. I would’ve had to crack open any of these engines and perform a valve job, maybe re-ring them, or even do a complete rebuild to get the kind of long-range reliability I was after. That adds time, money, and effort. The TBI search evolved into a TPI search, which evolved into a Vortec search, then on to Chrysler and then Ford V-8s.
Eventually I scrapped my whole search for older engines and moved on to more-modern options, which you’ll read about next month in Part II of this story. In Part III, I’ll introduce you to my choice of engine that’ll actually get swapped in front of my little Wrangler’s AX15 and start the install. Finally, Part IV will wrap up the install and give you a full drivability review, including mileage and acceleration numbers. Until then, here are some good junkyard engine swaptions for any Jeep model.
Chevy TBI 305/350
Years Manufactured: 1987-1996
Found In: GM put the LO5 350 TBI (throttle body injection) engine in just about everything. You’ll find the 210hp/300lb-ft engine in pickups, vans, Blazers, Suburbans, and cars like the Camaro or Caprice sedan and wagon. Most-commonly, you’ll stumble across the pickup models. The 170hp/255lb-ft L03 305 could be found in these chassis as well from ’88-’92, so be sure to check the rear of the block next to the distributor. The 350s will have a 5.7L and the 305s will have a 5.0L cast atop the bellhousing location. In ’93-’95 the 305 got a bump in torque, up to 275lb-ft, but horsepower remained the same at 170.
Pros: The injection system, sensors, and harness are very simple and easy to understand, which can make swapping easy. If you’re starting with a TBI-injected four-cylinder Jeep you’ll be able to use your stock in-tank fuel pump. Also, the low-pressure TBI system doesn’t require expensive high-pressure fittings and lines. And although it doesn’t look like a powerhouse on paper, the 5.7L LO5’s power and torque curves are very linear and come in right off-idle, resulting in an exceptional drivability and slow-speed off-road performance. Even the 305 makes for a nice upgrade that’s not a total gas hog.
Mounting: Advance Adapters and Novak Conversions make a plethora of bolt-in and weld-in motor mounts and/or engine crossmembers to physically get the engine in many Jeep chassis. Removal of the factory motor mounts would be required in any instance.
Mating: With some exceptions (Peugeot for example), if your Jeep came from the factory with a six-cylinder your existing transmission is up to the task of handling a TBI 350 or 305. Just use your head. Advance and Novak offer conversion bellhousings and bellhousing adapters for manual transmissions and adapter plates for autos. If you’re dealing with a four-cylinder, plan on swapping transmissions. You’ll find transmissions ranging from SM465 four-speed manual, TH400, TH350, TH700R4, and the 4L60E behind the TBI V-8s. Any one of these can be mated to a Jeep transfer case and makes for a very good off-road transmission.
Cooling: The radiator inlet/outlets are opposite from a standard AMC or Chrysler-era CJ, Wrangler, XJ, and so on. You could have the inlets and outlets moved at a radiator shop, but the cooling capacity of some factory Jeep radiators would be questionable with a V-8, so it’s usually best to go with an aftermarket conversion radiator as offered through Advance Adapters, Novak, or any one of a dozen radiator companies you can find on the web. Most often there’s a bolt-in solution. The factory GM mechanical fan can often be retained with good results, or a single or dual electric fan is another option.
Fueling: You’ll need either an in-tank or external electric fuel pump regulated at about 9-14psi. Due to the relatively low pressure, you can use injection-rated rubber hose with hose clamps where applicable.
Wiring: If you don’t have the skills or patience to separate the factory GM harness from the donor chassis, there are numerous aftermarket TBI harnesses available that will operate the factory GM computer, including Painless Performance, Rod Francis Wiring, Hotwire Auto, Speed Scene Wiring, Howell, Turbo City, and more.
Cautions: The factory TBI computer is a speed-density system that runs off pre-determined air/fuel tables. If you’re looking to modify your power levels with stuff like aftermarket camshafts, intake manifolds, head swaps, or even major exhaust modifications you’ll probably have to have a new chip burned to prevent the engine from running too lean and having detonation issues. Also, don’t try to run a 305 computer on a 350 and vice-verse. They just won’t perform correctly. If you’re going GM TBI it’s usually best to keep the mods to a minimum, or not mod at all.