Okay, maybe we're being a little harsh saying "dumbest engine swaps."
But saying "swaps that don't make altogether that much sense and are supplanted by alternatives that are more intrinsically facile" doesn't exactly roll off the tongue.
Granted, some of these swap ideas aren't exactly commonplace. And some actually have a cool factor that could outweigh the hassle and complexity of the swap. Nonetheless, they're swaps that we're asked about from time to time, so we feel the need to address them here. So before you grab the engine hoist and start ripping the diesel out of your tow rig for transplant into your flattie, or pull the trigger on that Viper V-10 from mopar.com, here's our take on the subject for the average reader.
The candidate: The 8.0L iron truck V-10 ran its course in 3/4- and 1-ton Dodge pickups from '94-'03. If you're contemplating an all-aluminum Viper V-10 take-out or crate engine, your pockets are deeper than most at-home swappers and you're probably having a shop do the work, so we'll concentrate on the 310hp/450lb-ft truck engines.
The perception: Gas is expensive and owners of these V-10 trucks that are getting long in the tooth are letting them go for $2,000-$3,000 which wraps all the needed swap components into one package.
The reality: Hey, it's a big engine with lots of packaging issues and it doesn't make a whole ton of power for its weight. Sure, the Viper engine is lighter and more powerful, but it's also exponentially more expensive. Although the aftermarket support isn't super-strong, Hotwire Auto (hotwireauto.com) will modify a factory Magnum V-10 harness for use in most Jeeps, but you'll still need to build motor mounts, upgrade the drivetrain, axles, suspension, and cooling to accommodate the additional torque, weight, and operating temps.
The exception: We've seen Wranglers with swapped-in V-10s that give a wow-factor that is good if you want to build a torquey show pony.
We think: If you're looking for that much additional weight and want 450-500lb-ft of torque off-idle, it makes more sense to consider a 454 or 502 GM or 460 Ford big-block. However, we do think the larger engine bay of an FSJ would make a cool home for the big V-10 and briefly considered going with a big iron Magnum V-10 in our Project J2008 '68 Jeep pickup.
GM 60-degree V-6
The candidate: GM stuck the little 2.8L piggy in everything from front-wheel drive cars, to S-10 pickups and Blazers, to Camaros and Firebirds. Later stroked to 3.1L and then punched to 3.4L, every version left any semblance of power, torque, and longevity at the door.
The perception: Why not yank a 2.8L out of a GM vehicle or '84-'86 Cherokee since they're plentiful in the junkyards? If it blows, you can grab a replacement pretty much anywhere. Or, why not upgrade a 2.8L Cherokee with a 3.4L Goodwrench 60-degree crate engine?
The reality: Even the "mighty" 3.4L GM crate engine offered as a power upgrade for the 2.8L puts out a measly 160hp and 194lb-ft of torque. Besides, reliability was never one of the 60-degree V-6's traits.
The exception: There is none. Move on.
We think: The 2.8L is so bad and underpowered it must've been designed by the French. Its only saving grace is that it shares the same bellhousing bolt pattern as Jeep's 2.5L four-cylinder. We'd rather have one of those.
4.6L Ford Mod Motor
The candidate: Ford began installing its new overhead cam 4.6L engines in '91 and had gradually phased out the older pushrod V-8s by the mid-'90s with 4.6L and 5.4L V-8s and 6.8L V-10 two-, three-, and four-valve versions of the engines. The 5.4L truck engines are powerful, but the more-common 4.6L versions found in standard Mustangs, Town Cars, and Crown Vics are sort of dogs, with power levels in the low- and mid-200hp range.
The perception: Since these engines litter the boneyards nowadays they represent a great high-revving source for a fuel-injected engine.
The reality: There's very little aftermarket support for the 4.6L, 5.4L, and even 6.8L engines in the way of wiring harnesses, stand-alone ECUs, motor mounts, and other components that would ease in swapping. Furthermore, the overhead cam design of these engines translates into an exceptionally wide package that's sure to have interference issues in most engine bays. And despite the perception, the 4.6L and 5.4L doesn't like to rev any more than most standard V-8s. It's just that they make comparatively poor torque down low in stock trim, so you really have to wind 'em up.
The exception: Perhaps if you scored a supercharged 5.4L out of a Lightning pickup or Cobra Mustang the hassle of figuring out the wiring and ECU and fitting it into the chassis would be worth it, but otherwise check earlier 5.0L Mustangs or 5.8L trucks if you've got a Ford fetish.
We think: There's no wow factor and no really good reason to run a Mod Motor.
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.
Jeep 134-cube F-head
The candidate: Introduced for the '50 Willys trucks and put into the '53 CJ-3B, the 72hp/114lb-ft (high-compression versions made 75hp) 134-cube Hurricane F-head offered 12hp and 9 lb-ft more than the Go Devil L-head it replaced. With the intake valves moved from the block to the head, the F-head could breathe much more freely than the L-head.
The perception: It's nearly a bolt-in swap that will up the power over the older L-head and help a stock(ish) Willys maintain speed on grades. It delivers 20 percent more horsepower and nearly 10 percent more torque.
The reality: It's all true. However, nowadays there are other ways to get drivability out of your L-head and better swap candidates that don't use antiquated parts like the F-head and don't require a special carb or a hole to be cut in the hood for carb clearance.
The exception: We're totally down with an F-head swap if you're building a period-correct '50s/'60s-vibe retro wheeler.
We think: It's better to save the F-head for a resto job on a CJ-3B or early CJ-5 or CJ-6. If you want power in your L-head-powered flattie, why not be different and slap a 2.2L Chrysler turbo on your L-head, add a Pertronix electronic ignition, and a one-barrel TBI injection? Or, if you're really good with swapping in a different four-banger, why not run a 2.3L Pinto engine, or better yet, swap in a 2.5L TBI or MPI Wrangler or XJ engine? Use a 2.8L GM V-6 bellhousing and put an SM420 behind it and never worry for power or drivability off-road again.
Chrysler/Jeep 4.7L V-8
The candidate: The Chrysler 4.7L overhead cam first saw Jeep duty in the '99 Grand Cherokee and wormed its way into the Dodge Dakota and fullsize Ram platforms as well.
The perception: For under $3,000, I can pick up a thrashed Grand Cherokee with the 4.7L and five-speed auto tranny and put it in my trail Jeep.
The reality: Have you ever looked under the hood of a 4.7L-powered Grand Cherokee? Besides looking like a nightmare to extricate, the WJ's overhead cam 4.7L is super-wide, very complex, and only puts out around 235-265hp. And again, there's very little in the way of aftermarket harness and ECU support to make the swap easy.
The exception: We really can't think of any.
We think: If you want modern V-8 power, you'll be way better off finding a wrecked Silverado and nabbing the 5.3L Vortec engine instead.
The candidate: In '93, grannymobile Cadillacs began running GM's premier DOHC 4.6L Northstar engine. With dual overhead cams, four-valves-per-cylinder, and an output of either 275hp/300lb-ft (LD8) or 300hp/295lb-ft (L37), the all-aluminum Northstars combined light weight, high strength, and smooth power delivery in one iconic package. The catch was that up until the LC3 came along in '07, all Northstars were transversely-mounted in front-wheel drive applications.
The perception: I'll buy a '90s Caddy for $800, yank the engine, and slap it in my Wrangler and go!
The reality: The transverse-mounted architecture is a nightmare to overcome. For starters, the log-style oil pan can't be chopped into a rear-sump design. Then, the intake manifold must be turned 180-degrees on the engine and the water pump manifold and water pump removed from the rear of the engine and replaced with an electric water pump for firewall clearance.
The exception: The engine architecture works well for rear-engine sand rail applications and, indeed, these engines are supported with aftermarket wiring harnesses and stand-alone ECUs.
We think: Leave 'em to the buggies. If you really need a DOHC Northstar, go find yourself an Olds 3.5L Shortstar V-6, add a turbo, and pretend you're running the V-8.
The candidate: The Jeep 4.0L was first put into XJs in '87 and upgraded to H.O. status with a better head and injection in '91. Used in Jeep Wrangler, Cherokee, Comanche, and Grand Cherokees for over 20 years and as durable as an anvil, there's no shortage of good swap candidates.
The perception: I'll take my 2.5L Jeep and just slap in a 4.0L.
The reality: Yeah, you can. Buy why would you? You've got to cut off the 2.5L engine brackets from the frame, weld on new 4.0L brackets, change out the front accessory package, modify or completely replace the wiring harness, swap out the transmission, clutch, and T-case input gear, change the tranny mount, rework the complete exhaust system, radiator hoses, ECU, and more. The only way it makes sense is if you have a complete donor sitting next to your Jeep and then, isn't it easier to just put your lift on the donor?
The exception: We can see doing the swap if you've got extensive chassis modifications and/or extensive cage and tubework done to your vehicle. But then, wouldn't you just go with a V-8 instead?
We think: You're still better off selling your 2.5L Jeep and buying a 4.0L Jeep if you're stuck on having the inline-six.
3.9L Cummins 4BT
The candidate: The four-cylinder 3.9L Cummins 4BT engine can be had in normally-aspirated, turbocharged, or turbo/intercooled versions and puts out 105-135hp and 275-350lb-ft depending on year, model, and what's been done to the fueling.
The perception: The more-compact 4BT will make any Jeep a real econobox commuter without giving up insane off-road crawling grunt and offers little-to-no packaging issues.
The reality: The 4BT is easier to fit into most Jeep engine bays and will deliver great mileage numbers on the road if gearing is carefully selected to keep the rpms down. But again, the noise, vibration, and fumes from one of these little paint shakers will be enough to push most Jeep owners over the edge of the nearest cliff. Plus, they weigh a little more than an all-iron big-block. They sound good on paper, but when you've lived with one of these conversions for a little while the buzzing and belching can really test the temperament of some drivers.
The exception: In the May '07 issue we featured Dave Smith's '80 J-20 pickup with a 4BT and Ford ZF five-speed tranny, and we've run into New Mexico's Jeff Wood's 3.9L-powered CJ-5 on the trail for more than a decade in one variation or another. Conversions like this do work, but in the end the success of such a swap is really more about the temperament of the owner/driver than the engine itself. It's only the right engine for the right driver.
We think: They're great, durable little mills that make good torque, but not a lot of power unless modified. For those with more refined tastes, a CRD from a Liberty would be easier to live with on a day-to-day basis, but there's no denying the dirt-simple engine management of the 4BT that will surely continue to hook prospective swappers. Trasborg sharply disagrees, but we have noted a difference in drivability between the 4BT and the 2.8L CRD in the small diesel Jeeps we've driven and ridden in.