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Old 11-21-2004, 08:46 PM
fire power's Avatar
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HEMI 331 354 bore size

I have read before about putting 354 pistons in a 331 ,cant find the bore size listed for the 354, how big do you have to bore and is there really enough meat to really get away with it safely, I seem to remember it takes a special head gasket, or maybe you just use the 354 one. Any body really know the TRUE skinny on this Thanks ahead of time firepower

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Old 11-21-2004, 10:44 PM
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331/ 354 Hemis

The 354 has a bore of 3.9375, dont have a spec on the other bore.
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Old 11-22-2004, 12:25 AM
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Thanks keith, a 331 is 3.8125, I seem to remember around .1oo differance and thats .125 , just dont know if thats a risky bore or not Ill keep checking firepower
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Old 11-22-2004, 12:34 AM
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Don't know the answer to that one but these guys most likely do. They supply almost anything you'll need in the way of obsolete engine parts. egge.com.
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Old 11-22-2004, 01:46 AM
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Thanks for the reply I just found a site that clears up a few questions . THeHemi.com. lots of all hemi info I couldnt remember
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Old 11-22-2004, 06:41 AM
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In 99% of cases there is enough meat in a 331 to bore it to 354 specs. The early hemis were all pretty thick wall castings and unless the block shifted significantly during the casting process you'll have no problems. That said, because you stand to invest a fair amount of money in any hemi rebuild I would suggest having the block sonic checked first just to be sure. There is that 1% chance and you don't want to ruin a perfectly good block if that's the case. Also if you're going racing, don't do it with a 331 or any hemi bored that much over. It's fine for street high performance use but not for an all out race motor.

When boring a 331 to 354 specs you have to keep in mind that in '55 the water passages in the block were altered slightly. Also you can't use a stock head gasket since the sealing lip on the stock gasket will fall into the cylinder instead of being compressed by head/block contact. The head will still contact it on the top but the cylinder is missing 1/16" of bore and that's the section that would normally compress the head gasket sealing surface. The solution is to use a 1956 354 head gasket. It will have the correct bore size and the water passage openings will align close enough not to cause serious problems. The only difference is that the dowel pin hole on the 56 gaskets is slightly smaller than the dowel pin on the 331 engines. All that is required is to open up the dowel pin hole on the gasket a few thousandths. There used to be a Fitzgerald gasket (#0559-SR) that was specifically made for this purpose. I don't know if its still available though.

Good luck.

Centerline
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Old 11-22-2004, 08:39 AM
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331 piston is 3 13/16", 354 is 3 15/16". All Chrysler did was bore a 331 1/8" over to ge the 354 in the first place. That is exactly what I had done to my 331. Ernie Hashim, legendary hemi guy and Bakersfield native did my engine work. He found a couple of stock 354 piston sets and made one good set from them. He bored the block and balanced the crank for me. Most parts are interchangeable between the two engines since they are otherwise virtually identical. Incidentally, the 392 is a bigger block w/ 1/2" taller decks on the block.

As fear as head gaskets are concerned, I don't think 331 gaskets are available any longer. Anyway I haven't been able to find any except NOS on ebaY. The stock 331 head gaskets are a single layer steel shim that require sealant on both sides. I don't like that style - never could get them to seal properly. 354 head gasket fit fine except for the push rod holes. On the 331 they are round but on the 354 gasket they are tear drop shaped and the point of the tear drop extends up past the head exposing it to severe oil leaks. To fix this I cut little tabs of asbestos gasket material for each gap and silicone it up really good. Once bolted in place they seal fine.
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Old 11-22-2004, 05:30 PM
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Another Site

http://www.classichemi.com/index1.shtml

also do a search for "Hot Heads" or something like that, they make LOTS of stuff for early hemi's
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Old 11-22-2004, 06:06 PM
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331 3.8125 x 3.625
354 3.9375 x 3.625
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