BigBird720

hey i have an 81 trans am with a 455 engine swap out of a 1972 GTO. i want the compression ratio to match the 1970 GTO due to the extra 36 horse and 85 ft lbs of torque it had. the 72's ratio was 8.4:1 where as the 70's was 10.25:1 so i was wondering if anyone knew how to go about that. thankss

joelster

Simply upping the compression isn't going to get you 36 horse and 85ft lbs of torque. I don't know the specifics exactly on those motors, but I guarantee they had different cylinder heads with different combustion chamber volumes, which made the compression ratio different. They probably had different camshafts too. Do some research and find out the volume in cc's of your combustion chamber. Then look at some aftermarket heads (Edelbrock, plus a few others) with smaller chambers to up the compression. A new aftermarket head will be substantially better than a '70 head, and will certainly net you more than 36 hp/85 ft lbs, with a proper camshaft.

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1994 Z28 Black heads/cam th350 drag car
1995 Z28 Teal 'Vert bolt-ons 6-speed cruiser

joelster

Ok, I did a little digging for you.

There were 2 455's offered in '70 both had 87cc chambers

There were 3 455's offerred in '72. The first one was the 455 HO it had 111cc chambers
The other 2 had 114cc chambers.

There is your compression difference right there. Good luck finding a set a 1970 455 heads though, they are rare and they will be expensive. Going by the casting numbers from the site i found, they were a one year only deal. 9799615, and 9799364 were the 1970 casting numbers. I think some aftermarket heads would do you wonders.

The Edelbrock heads come in 2 diiferent chamber volumes a 72cc size and an 87cc size. They flow about 40cfm more than the best Pontiac head the RAIV from the factory.

I found another specialty place that manufactures aftermarket Pontiac heads. It's called KRE, Kaufman Racing Engines. They make 2 different castings fro Pontiacs, a race high-port version, and a street/strip d-port version. The d-port has options for chamber volume up to 85cc. The pricing is similar to the Edelbrocks, expect to pay around $1700 or so fully assembled.

Tin Indian Performance - KRE Aluminum D Port Pontiac Heads

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1994 Z28 Black heads/cam th350 drag car
1995 Z28 Teal 'Vert bolt-ons 6-speed cruiser

BigBird720

thanks guys i appreciate the help