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07-19-2017, 07:51 AM | #18 | |
Registered User
Join Date: Dec 1999
Location: Austin, TX, USA
Posts: 7,717
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Re: how rare is factory AC?
There were no high performance high compression big blocks in the trucks. The only real difference between the 396 and 402 is a .030 overbore. And on the GMC trucks, they list the big block as "400" on the SPID. Same motor. The combination of pistons and combustion chamber dictate compression ratio. Closed chamber heads used different domes than the open chamber but the were all 8.5:1.
I just built a 390hp 427 for my '69. It's also a '69 from a 'vette. 512 2 bolt block and 290 101cc heads. Should be right at 10:1 with the SpeedPro pistons that are the stock replacement spec. I have a second 427 with the same pistons and a set of 781 heads that should put the motor at 9.3:1 because of the 118cc chambers of the later open chamber heads. Quote:
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44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax |
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