CJ5 Engine Swap Choices
Article by Mark Trotta
Early CJ Jeeps (1954 to 1969) weigh about 2,200 pounds and have a short wheelbase. The best choice for an engine swap is not a V8.
Aside from requiring too many modifications, it'll have more power than the rest of the vehicle can handle. And the fact that there just isn't a whole lot of room under the hood, a V6 or even a modern four-cylinder are clearly better choices.
Drivetrain Concerns
The stock Jeep drivetrain is rated at just 1/4 ton, which is roughly 500 pounds load capacity. To handle V8 power adequately would require replacing the transmission, axles, etc. Plus, the stock (50+ year old) frame wasn't designed to handle that power. You'd end up with a top-heavy vehicle that just spins tires.
Off-Roading Concerns
If you're planning on taking your Jeep off-road, be it mud or dirt or gravel, remember that speed isn't a factor. The added weight of a V8 on the front suspension will make for slower maneuvering, plus you're more likely to sink into mud (have a winch ready).
SBC Engine Weight Highest to Lowest
For comparisons sake, Gen I and II small block Chevys weigh about 550 pounds.
A Gen III small block Chevy weighs about 470 pounds.
An LS1 Chevy weighs about 407 pounds.
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V6 Engine Swap
A V6 engine will give you all the power that a lightweight, short-wheelbase Jeep can handle. Additionally, a V6 configuration (versus a straight six engine) makes for a relatively compact motor, which fits easier into a tight engine compartment. This is of particular concern with early flat-fender models.
The two most common Jeep V6 engine swaps are the 225ci Buick and 4.3L Chevy.
A 225 Buick 90 degree V6 (odd-fire) weighs about 375 pounds.
A 4.3L Chevy weighs about 425 pounds.
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Buick V-6 Engine
Offered in 1966 Jeep CJ and C101 models, the Buick-designed "Dauntless V-6" displaces 225 cubic-inches and produces 155 horsepower in stock trim. That's nearly double the output of the original Jeep four-cylinder engine. Since this motor was offered optionally in CJ models from 1966 through 1971, it's a fairly easy install.
The block and cylinder heads of the 225 V6 are cast iron, and the motor is externally balanced. The valve lifters are mechanical, so they'll need adjustment from time to time.
The 90 degree V6 Buick's firing order, 1-6-5-4-3-2, is known as an "odd-fire" pattern. The heavier, thicker original flywheel must be used in Jeep vehicles, which increases torque and helps dampen vibrations of the odd-fire design.
Chevy V-6 Engine
Another popular engine swap choice for early Jeeps is the 4.3 litre Chevy V6. Introduced in 1985, this motor is basically a small-block Chevy V8 with the back two cylinders cut off, so parts availability is excellent. Plus, it's compact size fits well in vintage Jeep CJ's.
Made by Trans Dapt, these Bolt-in Motor Mounts for 1976-1983 CJ5 will accommodate Chevy V6 and Gen I small-block V8 engines. They also fit 1976-1986 CJ7, and 1981-1985 Scrambler.
Also offered by Trans Dapt are weld-in motor mounts.
NOTE: A popular engine/transmission combo is a Chevy 4.3 V6 with a GM TH350 automatic.
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AMC 2.5 Four Cylinder
Back in the day, our 1989 Jeep Wrangler was powered by an AMC 2.5L motor. It was reliable and got decent mileage, but I found it to be under-powered on the highway, but great for around town or off-roading.
Any AMC 2.5 engine will accept GM small V6 and four-cylinder bolt pattern bell housings. These bell housings are found on many GM transverse-mounted engines.
Another popular engine/trans combo is the AMC 2.5L motor and Borg-Warner T-5 transmission.
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AMC 4.0L Straight-Six
If the AMC 2.5L had two more cylinders, it would be the 4.0L motor. These motors were installed in Jeeps from 1987–2006, making them plentiful and cheap. But at 480 pounds, they're kind of heavy.
AMC 4.2L 258
The 258 straight-six is also a great motor, but again, too heavy for a CJ5. Early 258 motors weighed about 540 pounds, and ones produced after January 1980 weigh around 480 lbs, which is about the same as the 4.0 motors.
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Four Cylinder Iron Duke Engine
Produced by the Pontiac Motor Division from 1977 to 1993, the 2.5L (151ci) "Iron Duke" was the predecessor of the AMC 2.5L engine. In the eighties, GM began selling the engine to AMC for use in Spirit, Concord and Eagle models, and also in base-model CJ's. The engines in AMC vehicles continued to use the Chevrolet V8 bell housing pattern.
Several significant changes were made to the Iron Duke motor in 1987, including an improved cylinder head and serpentine belt with an automatic spring-loaded tensioner. Through the years, power output went from 85 horsepower up to 110 horsepower.
Installing The Motor Is Only The Beginning
Installing different engine mounts and bolting up the motor is only the first step in the engine swap process. After that, a multiple series of "mini projects" begins, including hooking up the transmission, cooling and exhaust systems, and wiring it all up.
At this point, you may consider upgrading the brakes and suspension.
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Transmission Choices
No engine swap discussion is complete without talking about transmission compatibility. The following are manual transmission choices:
Borg-Warner T14
The B-W T14 transmission is a light-duty, manual three-speed, and offered in Jeeps through 1975. It served as the base transmission with AMC 232 and 258 I6 engines.
The T14 transmission is 8-11/16" long and the main case is cast iron. If needed, companies such as Novak offer adapter assemblies.
Borg-Warner T15
The B-W T15 is a medium-duty, manual three-speed transmission. Not only was it offered in CJ Jeeps through 1975, it was also found in full-size Jeeps through 1979. The T15 was fitted behind AMC V8 engines as base transmission, and optional with AMC 232 and 258 I6 engines.
Borg-Warner T18
The B-W T18 transmission is a heavy-duty, manual four-speed, and also found in various Jeeps, Ford trucks and I-H trucks. The T18 is synchronized in 2nd through 4th gears.
GM Muncie SM420
The SM420 is a heavy-duty four-speed manual transmission. It was produced by General Motors and found in light- and medium-duty trucks from from 1947 to 1967. The SM420 also saw use in U.S. Military vehicles as late as the early 1980s.
A standard Buick V6 bell-housing will bolt up to an SM420, making that an easy transmission swap. Installing an SM420 behind other motors will require an adapter, which can be obtained by companies such as Novak.
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Conclusion
A four-cylinder engine will provide adequate power for off-roading and around town driving. It will also give you the best fuel mileage that you can get from an old Jeep. But for those who do a lot of highway driving, or want better acceleration, a six-cylinder would be a good choice.
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Related Articles:
Engine Swap Basics
Best Old Jeep To Restore
Jeep CJ History (1970-1986)
6-Volt To 12-Volt Conversion
