Question: What Engine/Transmission Swap Belongs In the '41 Plymouth?

Murilee Martin
by Murilee Martin
question what engine transmission swap belongs in the 41 plymouth

Since my brain threw a code and made me buy the 1941 Plymouth Special Deluxe Junkyard Find yesterday, I need to choose a suitable modern engine and transmission combo for the thing. I’ve hired a rocket scientist and weirdo hot-rodder (the lunatic who built the Rocket Surgery Racing mid-engined Renault 4CV) to execute a chassis modernization program on the old Mopar, and I need to make my drivetrain choice ASAP. Suggestions?

Much as I’d like to go with a 2,500-horse Chrysler IV-2220 engine for this project, I need to stay on a fairly strict budget, say $2500 for engine and transmission. Most likely I’ll buy a complete donor car and truck, grab the engine, transmission, driveshaft, computers, and any other goodies needed for the swap, then sell everything I can on eBay and feed the rest to The Crusher at $250/ton. It would be (slightly) nice to stay within marque and go with a Chrysler engine, but I also like the idea of enraging the purists— you know, the guys who have those creepy Time Out Kid dolls leaning on their numbers-matching Road Runners at car shows. So, before everyone starts yelling about how I should get a 440 and Torqueflite 727, problem solved, let’s go over some of my requirements and preferences for this swap:

1. This car must have a manual transmission. Sure, I’m going to drive it on the street and take it to the drag strip, but this car is going to be set up for road racing and taken to track days at my local track. You don’t need a manual transmission for that, and I’m not a sufficiently fast driver to get the extra couple of seconds per lap a manual transmission might give you, but you’ll have a lot more fun with a stick. Long-term, I plan to enter it at Pikes Peak and, if I get really crazy, the Carrera Panamericana. I’m willing to contemplate the idea of swap bellhousings, weird adapters, and the like, but the easiest solution is to get an engine/transmission combination that came together from the factory.

2. The engine must fit a narrow prewar engine compartment. There’s not enough room under the ’41 Plymouth’s hood for a typical 90-degree overhead-cam V6 or V8 engine to fit without fabrication hassles beyond what I am willing to contemplate. That means the excellent Ford Modular V8 is out, which eliminates the tempting Lincoln Mark VIII DOHC engine/Tremec 3550 transmission idea. The fairly narrow Toyota UZ engine might fit (barely), but bolting a manual transmission to one— as done by many drifters already— requires the application of cubic dollars. The BMW S62 V8 is also fairly compact, and manual transmissions are readily available in crashed E39s, but the computer nightmares with these engines are legendary to put it mildly. The most likely candidates at this point are Detroit pushrod V8s and screaming Japanese or German L6s, though the idea of a hopped-up GMC 292 L6 lurks at the edges of this discussion.

3. The engine must have potential for non-insanely-expensive bolt-on power upgrades later on. This could mean that the engine has a vast aftermarket of quasi-affordable performance add-ons (e.g., turbocharger/supercharger kits, better heads, stronger rods, and so on), or it could mean that related engines can be swapped in without cutting anything. I don’t plan to go above 400 horsepower or pound-feet (the point at which the differential I’ll be using— that’s a secret to be revealed later— becomes the weak link), and 250 horses will be fine to start with.

4. The engine must have electronic fuel injection. Even though I’ve been on this planet as long as my ’41 Plymouth has been sitting in a Colorado field, I don’t subscribe to the curmudgeonly view that carburetors are good. That means the best engine candidates come from vehicles built in the early 1990s or later. If absolutely necessary, I’m willing to apply Megasquirt to an engine, but my very strong preference is to use all the factory computers, sensors, wiring, everything. Buying a complete donor vehicle makes the most sense for this approach, which means that I need to take into account the resale value of the donor vehicle’s leftover parts.

5. No Hemis. No LS engines. The going rate for an LS with T-56 or TR-6060 transmission, yanked from a GTO, CTS-V, or Corvette, is $5000-$8000 and up. Way up. You can get early 5.7 Hemi engines out of Dodge Rams for much cheaper, but they came with slushboxes exclusively and you’ll spend your louie in a hurry getting a sufficiently beefy manual transmission attached to one.

6. I really want an overdrive transmission. I’m going to be running a fairly wild (4:1 or shorter) differential gear and I plan to take this car on highway road trips, which means screaming along at four grand at 60 MPH isn’t going to cut it. Thus, no 833, Muncie, or Toploader 4-speeds. No, I don’t want an overdrive 833 4-speed.

At this point, my top choice is the Chrysler Magnum 5.9 (aka 360) engine, descendent of the venerable LA family of small-block V8s and available in Dodge Ram 1500s and 2500s with the NV3500 5-speed manual transmission. The 360 is a great engine, it’s within marque for the Plymouth, and performance parts are cheap. The problem here is that it is virtually impossible to find a two-wheel-drive Dodge truck with a manual transmission (I’ve been beating my face against an online-search brick wall for weeks, and that’s with a willingness to bring a donor vehicle back to Denver from two-wheel-drive places like Omaha or Lubbock). NV3500s are commonplace in junked V6 Dakotas, so I could do the wrecked Ram Van + junkyard transmission + 360 flywheel + ECM from a manual-equipped 5.9 truck equation, but that’s a lot of hassle for a truck transmission that starts to get explode-y at 350 ft-lbs.

My second choice, but gaining ground in a hurry, is a GM LT V8 engine with Borg-Warner T-56 transmission. In other words, buy some hooptied-out-but-strong-running fourth-gen Camaro Z28 or Firebird Formula for $2500. This gets me a 275-horsepower motor with near-limitless hop-up capacity plus a very nice road-race transmission that can handle big power… but it also means I’ll be the 900,000,000th person to drop a small-block Chevy into this kind of project car, plus there’s the whole Optispark ignition headache. In terms of bang-per-buck, you just can’t beat this setup, and the logic of using it is the same one used by hot-rodders in 1948 who put flathead Ford V8s in everything, but I’d prefer to be a little oddball here.

I’m just beginning to research the idea of a Vortec 5300, 5700, or 6000 V8 with manual transmission, a combination theoretically— though probably not in practice— available in 2WD Chevy Silverado/GMC Sierra trucks. The Vortec makes great power, but the manual-transmission options appear to be the pure-truck, granny-gear-equipped NV4500 and ZF-S6-650 and some 5-speed that I’m guessing is either the NV3500 or the even more fragile T-5. Anybody who knows more on this subject, or even anyone who has seen a two-wheel-drive/manual-trans/V8 Silverado on the street, please share your info with us in the comments.

The real wild card here is the idea of buying a bashed BMW 540i with factory 6-speed and facing the horror of turn-of-the-century BMW computers. You can find these cars in ugly-but-running condition for two or three grand, the engine is much lighter than Detroit iron-block V8s, the Getrag 6-speed is a joy, and I know the 282-horse M62 V8 engine will fit in a BMW E30 (there are two of them racing in the 24 Hours of LeMons and, yes, I hammer them with penalty laps despite being butt slow due to handling problems) and thus is quite narrow. On the downside, there is no cheap way to add power to this engine, and the hassles involved with making BMW computers behave are so severe that anecdotes about them are not mingled with ordinary stories of problems with automotive electronics.

What else? Turbo Buick V6 with absurd boost and hope-it-lives T-5 transmission? Big L6 out of a Detroit truck, equipped with centrifugal supercharger? Mercedes-Benz M104 six? Something I haven’t thought of? Rack your brains!

So, here we go! I will be reading your comments and advice closely as I prepare for a new round of donor-vehicle shopping. Mujahideen of the Mopar Jihad (I picture you driving your Oerlikon-equipped Ramchargers through the Khyber Pass while sneering at those fools in their weak-ass Toyota Hiluxes), feel free to inform me of the hair-raisingness of the fatwas to be issued on me by your warlords, should I choose to run a GM engine in a Plymouth.

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  • Nick Nick on Dec 09, 2012

    Would a small, low deck early Hemi fit? Either a 241/270 Dodge or a 276/291 DeSoto? You should really stick to Mopar. These guys http://www.hothemiheads.com/ can sell parts to make it a good performer. Failing that, a built up225 /6. I've seen one in a Dart with 240 RWP without forced induction or anything.

  • Pragmatic Pragmatic on Dec 09, 2012

    Go for a hemi out of a Challenger these were available with 6MT. Not sure it could be had for your budget.

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