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What engine do I put in my 1936 Plymouth

The original engine in my 36 Plymouth has been replaced with a 350 Chevy with a 350 Auto trans. The car gets terrible mileage and the trans has been rebuilt 3 times, leaks, and still isn’t right. If I were to start over and put a reliable engine that gets good mileage, what would it be. (I’m not looking for a street rod, just a daily driver).

I would put in a fuel injected engine from a modern vehicle. Not only do you get better mileage, but the fuel system should be able to handle the ethanol used in gasoline today.

I have a friend with a 1953 Ford F100 pickup and went to fuel injection for this reason.

Here’s the engine in the vehicle.


As frustrating as your current setup is, you might want to save BIG money and upgrade it, rather than get rid of it. What condition is the engine in? Miles? Compression? You could put on an electronic fuel injection system and electronic ignition that should improve your mpgs and drivability. A good tranny shop should be able to take care of the leaks.

How many miles a year do you want to drive it?

You will never get good mileage from this beast. If your commute is a good distance they pick a different daily. Going with a smaller v8 might not be good either. It must work harder to do the same.

350 fuel injected

I agree with texases. As long as the 350 Chevy engine is in decent condition, you can bolt on a standalone fuel injection system for a little over a thousand bucks. If you don’t have HEI already, I would upgrade that. You can probably find a junkyard or Chevy nut who has a box full of HEI distributors from the '80s you can get one from for a reasonable price. As for the transmission, I would quit messing with this one if you are really at your wit’s end and just get another one to put in there. Summit Racing sells fully rebuilt TH350s for less than a grand, or for a little more, you can stick a 700R4 in there and have an overdrive ratio for better mileage. Disclaimer: a 700R4 will bolt right up where a long tailshaft TH350 lived, but if you currently have a short tailshaft TH350, you will need a shorter driveshaft. All this will run you less than the modifications needed to make a different power plant work in this beast, unless you are a good fabricator and have the metalworking abilities and equipment necessary to make it happen. This is the primary reason I suggest pretty much keeping the setup the way it is rather than completely changing everything.

With the right rear axle, a good engine, carburetor set up properly, and tuning correct I don’t see why the car can’t be made to be acceptable in the mileage department.
The carbed 350s I’ve owned would get 20-21 on the highway and all of those cars had the TH350 transmission. With a 700R4 mileage would have been even better.
Jeez, even my old muscle cars (Roadrunners, Superbees, etc would get 17 on the road.

There has to be more to this story. A transmission has been rebuilt 3 times already and currently leaks?
Does it have the Quadrajet carburetor and just what kind of fuel mileage is it getting?\

Who in the world is building the transmissions and doing the engine tuning?

A heavy car with a v8 that gets terrible fuel mileage?! Say it ain’t so!
The 350 V8 and 3.8L V6 from GM are 2 of the most reliable engines GM ever built; they put them in just about everything.
What’s your definition of terrible fuel mileage? 8 in the city, 12? 15?

I’d leave the 350 motor and trans. The 350 is a reliable motor that can get at least 15MPG city/20+ HWY even with a carburetor. My friend’s 1972 Impala used to manage 17, not bad for a 2 ½ ton car with a points ignition. It may be there’s something wrong with the tuning or timing on yours. Plus a street rod isn’t exactly the most aerodynamic of vehicles. You will spend far more trying to put a smaller motor in this than you will likely ever save on gas, and you’ll lose some performance and responsiveness most likely.

The THM350 tranny likewise is a good transmission. If it’s leaking, then someone botched the rebuild or it needs some attention, not chucking in the dumpster.

Do you really want to drive a 1936 vehicle all the time? Sure it has mega cool factor, but you risk door dings, rust, probably no A/C and ride, handling, reliability, and safety that just isn’t up to today’s standards. I’d spend the money you would spend on mods for getting a second car and only drive the 1936 part time.

If mileage is what you want, I’d recommend a 3.8 v6. With a good transmission that has a locking torque converter, you could be looking at the high 20’s on hte highway.

Ah the ubiquitous 350/350 combo, the one that everyone and their brother uses for just about any restomod project. IMHO it’s only appropriate for use in a GM product. It’s one of my pet peeves to see the 350/350 in a Ford or Chrysler.

For your car I would go with a Chrysler Magnum 360 or 383 crate motor backed by torqueflite A727. But if you’re after fuel mileage a 318 would be a better option.