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RB67SS 03-06-2013 05:14 PM

piston identification
 
I have an 1980 era GM crate motor 454 the stamping numbers on piston dome are 3999295 with GM also i am running 118cc heads.. I need help with static compression? Thanks Randy B.

BOBCRMAN@aol.com 03-06-2013 05:34 PM

A bit under 9-1 depending on factory machining variants.

2speed_1 03-06-2013 05:39 PM

piston id.
 
this is from the GMPP catalog. 1971 LS-6 std bore 9:1 comp closed chamber pressed in pin i think the head cc's around 106 - 108

vinniekq2 03-06-2013 06:14 PM

LS-6? I thought they were 11:1? my LS-5 was 9:1

BOBCRMAN@aol.com 03-06-2013 06:49 PM

1971 was first year for low compression high-perf BBC

RB67SS 03-07-2013 09:30 AM

update cyl heads are 6272990 118cc open chamber with 3999295 pistons which are supposed to be for a closed chamber head ? any ideas on the compression ratio with this set up? Thanks Randy

BOBCRMAN@aol.com 03-07-2013 04:33 PM

990 head is similar cc to heads that were originally used with that piston. Hence the 9-1 rating.

cobalt327 03-07-2013 05:18 PM

Quote:

Originally Posted by RB67SS (Post 1654402)
update cyl heads are 6272990 118cc open chamber with 3999295 pistons which are supposed to be for a closed chamber head ? any ideas on the compression ratio with this set up? Thanks Randy

About 9.3 w/a 0.041" quench distance, 0.030" over 454, 118cc heads and the 14cc domes.


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