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Cadillac 331 engine interchange

Started by bigbry13, April 24, 2021, 10:24:29 PM

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bigbry13

Hi all,
I am looking to find a replacement 331 for my 51 Cadillac and I am wondering what years I can use as a direct swap? are 49-52 the same? are the 54-55 different? any input would be greatly appreciated. thanks a lot!
Bryan
Bryan

Jay Friedman

A direct swap would be any 49-51 engine.  You could use a 52-54 engine, but the cylinder heads and exhaust manifolds are different on these engines as the exhaust ports are bigger and the manifolds are set up for dual exhausts.  Your 51 exhaust manifolds would not connect properly to the 52-54 cylinder heads.

To adapt a 52-54 engine to your 51 you would have to either install a 2nd exhaust pipe on the left side or somehow fabricate a crossover pipe from the left side to connect with the right side exhaust pipe. 
1949 Cadillac 6107 Club Coupe
1932 Ford V8 Phaeton (restored, not a rod).  Sold
Decatur, Georgia
CLC # 3210, since 1984
"If it won't work, get a bigger hammer."

Jay Friedman

Bryan, 49-51 motors all have 160 hp. 

There are minor differences: the 50 and 51 intake manifolds and carburetors have small passages to the base of the carb that provide heat for, I think, quicker warm-up.  The 49 intake manifolds and carburetors don't have these.  Also, the 51 distributor is slightly different from the 49 and 50: the distributor cap is taller, as is the the cam that moves the points. 

Other than the above, as far as I know the 49-51 motors are the same.  What you could do is use your 51 intake manifold, carburetor and distributor which should fit and work perfectly on the 49 block. 

If, on the other hand, you obtain a 52-54 block, another way to use it with would be to install your 51 cylinder heads on it which I think would fit. 
1949 Cadillac 6107 Club Coupe
1932 Ford V8 Phaeton (restored, not a rod).  Sold
Decatur, Georgia
CLC # 3210, since 1984
"If it won't work, get a bigger hammer."

signart

IMO you would do well to seek a '53-'54 331 as they were developed as far as this engine family could of the ones that will direct bolt to your transmission & mounts. With these you would afford a very significant increase in horsepower with the higher compression, 4 bbl carb, etc. Dual exhaust would only enhance the power, economy, sound and coolness factor. A rebuild would not cost any more than building a '49.
Art D. Woody