Medium-Duty Diesel
The candidate: We're talking about the 5.9L or 6.7L Cummins, 6.6L Duramax, 6.2L or 6.5L GM, or 7.3L or 6.0L Powerstroke diesel engines.
The perception: For some reason guys think one of these engines will make any Jeep better everywhere from the trail to the street. Most expect exceptional low-end grunt in the rocks and mileage numbers on the street in the high 20mpg range.
The reality: These engines are without exception packaging nightmares in most Jeep chassis. Besides the fact most weigh in excess of 1,000lbs, the related turbo, intercooler, plumbing, and cooling components will put many swappers over the edge. The massive torque of most of these engines will require equally-massive axle and drivetrain upgrades, not to mention frame and suspension bolstering. Plus, comfort will suffer thanks to the immense vibration and exhaust fumes.
The exception: If you're starting with a home-built frame or grafting a body onto an existing 3/4- or 1-ton chassis it may go more smoothly. Or start with a larger candidate, like a J-truck.
We think: There's a wow-factor with a cleanly-done big diesel swap, but it's a deceptively-complex undertaking that will overwhelm most enthusiasts who try to tackle it themselves.
Ford Flathead V-8
The candidate: Back in the late '40s and early '50s the Ford flathead V-8 was the affordable alternative to the new (and expensive) overhead-valve V-8s like those offered by Oldsmobile and Cadillac. The '32-'54 Ford flathead belted out 85-125hp depending on model and year, which was a real improvement over the Go Devil's 60hp.
The perception: Old is new and the tattooed hot rod culture is en-vogue once again. It's retro-cool to slap a Ford flathead V-8 in a flattie using swap meet parts for a unique wheeler that'll turn heads when the hood is popped.
The reality: There's no denying the cool-factor of an old-school Ford flathead V-8 in virtually anything, but nowadays the parts to mate it to an early CJ's drivetrain are exceptionally rare, hard to find, and/or expensive.
The exception: In our travels we've come across a few genuine examples using old-school conversion bellhousing adapters, but don't hold your breath looking for one to surface.
We think: It's not a swap a casual admirer of the hot rod culture should undertake, but it's worth looking into if you've got the time, deep pockets, and conviction to make it happen. During a brief search we found a company called Flatattack Racing Products (flatattackracing.com) that manufactures a conversion bellhousing to mate '32-'48 Ford V-8s to a Toyota five-speed. This bellhousing could also be used to mate the flattie to an AX-15, which can be mated to a Spicer 18. As long as the suspension is kept at stock height there should be plenty of driveshaft to make it happen.