My brother, Dan, has a ’69 350 HO Firebird (100% stock) and I have a ’69 350 HO Custom S 4-dr sedan (also 100% stock) that each have measured 9.7 to 9.9 to 1 static compression ratio cold and 10.0 to 10.2 to 1 hot with the Whistler box. The Firebird is a 4-speed car, so has the factory 068 cam, and the Custom S is an automatic car, so has the factory 067 cam. Dan ran both engine set-ups on the DeskTop Dyno, and the 067 cam made the same hp as the 068, but with 10 lb-ft more torque. So, don’t over-cam your 350. Both cars have the std. 3.55 gears with the optional HD Safe-T-Track limited slip.
Dan built and dyno’d a ’69 350 HO intended for the Pure Stock Drags way back on 2006 with 10.6 to 1 compression and a 067 inspired custom ground cam (201/217/110 at .413”/.424” lift) that made 342 hp (@5300 rpm) and 403 lb-ft torque (@ 3700 rpm) through the log exhaust manifolds and 2.5” mandrel head-pipes.
Your ’75 350 4-bbl needs 9.0 to 1 compression minimum to run well with anything more than the 2800 Summit cam, which requires different heads like 16’s, 62’s, or 13’s with a chamber around 78 cc’s.
Dennis
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