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#35880 06/16/02 12:42 PM
Joined: Sep 2001
Posts: 4
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bmince Offline OP
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I am hoping a few of the Mopar fanatics could give me some advice on rebuilding the motor for a 1940 Plymouth sedan that I'm restoring.
I would like to increase the performance of the engine, without ruining reliability.

The engine is currently bone stock. I'm planning to keep the original trans. and rear. I'll probably convert the car over to a 12V electrical system.

A few of my questions are:

1. How can I improve the bottom end? Everyone tells me the flathead Mopars have very weak bottom ends.

2. What is the best way to improve the oiling system?

3. What is the best compression ratio, and how should I achieve it (pistons, mill head, etc.)?

4. What is the best carburetor to use?

#35881 06/17/02 01:51 AM
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Your car if original has a 201 ci eng.I'll share some of the things I did to improve my eng. I have a '38 Dodge bus.cpe w/the original eng. I took a '56 Ply.eng as a donor eng.(which was a 230 ci) removed the crankshaft and rods and installed them in the '38 block bored it .040 over and made a 234 ci,also used the '56 cyl.head which raised the comp. but I think the '57 head will raise it even more. I only milled the '56 head enough to make it straight. It seems that 2 and 5 rod journal may be the weakest from lack of oil. Hudson has mentioned this to me or on this site,maybe he will chime in on this with more info. Need to mention that the '56 shaft was something like 3/16 longer than the '38 shaft but it was all past the rear main and did not cause a problem for me. I also installed a T-5 5 speed manual o/d trans. Wasn't building a hot rod just a smooth ride.

#35882 06/19/02 05:06 PM
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Hey bmince, if you look at the topic below "flathead stuff" engines, there is some talk in there about performance mods. Also, if you look up at the right hand site of the screen, you will see that there is a drop-down menu that will let you select how far you want to go back to see previous postings (i.e., the last day, last two days, five days, month, hear, etc.). Choose to see postings from the last year, and you will find one topic that has 52 responses - "Let's talk flathead modifications". There are some good (very technical) messages in there regarding performance and I believe there are some regarding oil system mods, as well.

One suggestion is to balance your crankshaft, flywheel, pressure plate, rods and pistons. This will help the bottom end to last longer. As for oil system mods, you probably shouldn't need to make any such mods unless you are planning to run your engine above 3000 rpm for extended periods. A couple of things can be done fairly easily for some improvement, though. One is to buy a high-volume oil pump. I bought mine through Vintage Power Wagons for my 230 cid flathead. The other thing is to buy a stiffer pressure relief spring (green one). I also bought this from Vintage Power Wagons.

As for performance, there are a number of suuppliers in the "Links" section of the www.P15-D24.com website. These people supply cams, dual carb intake manifolds, and hopefully Vintage Hot Rod Parts will soon be supplying headers. Also, Crane Cams and Pertronix both supply electronic ignition kits that can be adapted to fit the flathead 6 distributor. You can also mill the head some for more compression.

Hope this helps.


Matt


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