what comp. ratio? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

GMC 3 · 12-30-2002, 07:27 PM

I am rebuilding a 350 + .060 and am reusing the pistons- they are in perfect condition- they are the stock style dish with 4 relief valves. what comp ratio will they give me with 64cc vortec heads. was thnking maybe about 8.5-9.0 but wasn't sure
thank you

**MikeB** · 12-30-2002, 09:22 PM

Depends on the size of the dish and head gasket compressed thickness. Your deck height also comes into play. Assuming an 18cc dish , .038" gasket, and stock deck height (not milled), a .060 over 350 should be about 8.7:1 with 64cc heads. There's a CR calculator at http://www.rosspistons.com/CR%20Calculator.htm

Detroit Gasket makes a 028" composition gasket that will bump it to 8.9:1. I wouldn't use thinner steel shim gaskets unless your deck and head surfaces are perfectly flat.

12-30-2002, 07:27 PM	#1
GMC 3 Registered User Join Date: Dec 2001 Location: Philadelphia, pa. U.S.A. Posts: 87	what comp. ratio? I am rebuilding a 350 + .060 and am reusing the pistons- they are in perfect condition- they are the stock style dish with 4 relief valves. what comp ratio will they give me with 64cc vortec heads. was thnking maybe about 8.5-9.0 but wasn't sure thank you

12-30-2002, 09:22 PM	#2
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,475	Depends on the size of the dish and head gasket compressed thickness. Your deck height also comes into play. Assuming an 18cc dish , .038" gasket, and stock deck height (not milled), a .060 over 350 should be about 8.7:1 with 64cc heads. There's a CR calculator at http://www.rosspistons.com/CR%20Calculator.htm Detroit Gasket makes a 028" composition gasket that will bump it to 8.9:1. I wouldn't use thinner steel shim gaskets unless your deck and head surfaces are perfectly flat. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!



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