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boatanchors 11-15-2008 11:47 AM

street big block compression
1971 454 2 bolt main. i was just curious is the compression limit on a big block before running higher octane fuel was the same as a small block. or if it would be higher like 12:1 or lower like 8.5:1. i know im not going to ride the edge on my compression but whats the average on a pump gas streetable big block?

Packard V8 11-15-2008 12:22 PM

FWIW, figure a typical performance BBC needs .5 to 1 point lower compression than an equivalent SBC/SBF, due to the larger bore and the more open chamber. Obviously, on a BBC, a 4.600" bore with aluminum open chamber heads is different than a 3.937" bore truck engine with closed chamber iron heads.

thnx, jack vines

boatanchors 11-15-2008 12:52 PM

would it be possible to run a BBC on pump gas with 12.8:1 compression or 12:1?

Packard V8 11-15-2008 01:01 PM

If the cam duration is long enough to bleed off some compression at low RPMs. Naturally, that much cam duration loses low speed power and fuel economy.

A better real world measure is cold cranking compression. If everything is right, you can run 200PSI on 91 octane, IF you have aluminum heads and IF the carb and distributor tune are spot on and IF you have a low rear gear.

thnx, jack vines

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