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Author Topic:   compresion ratio
85firebird
Member
posted September 02, 2003 07:44 PM
How small? 1.72"? 1.84"? 1.94"?

With flat tops, 54cc will get ya around 11:1. 82-85 305 HO heads had 1.84" and 1.5" valves and were the only 'performance' 305 head ever and had 52-55cc chambers. They came in Camaro's and F-birds with the carb 305 HO. 1.94" and 1.6" valves fit perfect and will run up to about 5800-6000.

Each point of compression is worth about 4% power across the board.



xx RACER 96
Member
posted September 05, 2003 02:21 AM
Along the same subject, how much compression is minimum for alcohol and how much is optimum?


85firebird
Member
posted September 05, 2003 06:40 PM
I've got 350 heads w/194-150 valves and I was wanting to bump up the compression. Will a 11-1 motor run good with small valve heads or are the small valves hurting it. I wont put 305 heads on a 350 unless I absolutely have too. I will probably get 202-160 valve 64cc chamber heads for the new motor in the works I just want to get all I can out of what I have now. 350 (40) stock crank rods w/arp bolts 76cc heads 194-150 cast iron intake 4412 carb .480 lift cam int+exh. The heads are just for know and I plan on upgrading SOON.


xx RACER 96
Member
posted September 06, 2003 01:39 AM
With 11-1 compression You shouldn't expect any real power gains over gas, the advantage would be a much cooler running engine. If you choose to run alcohol in a engine under 11-1 you should expect to loose some performance. Optimum compression for alcohol would change depending on your combination. My preference is to run at least 13.5-1 compression and as much as 15.5-1 compression with alcohol. With good compression and an adequate fuel system (very important) you can expect some real gains over gas.


xx RACER 96
Member
posted September 06, 2003 01:53 AM
Spend a little money on a good valve job and the small valve heads will get you by just fine, concentrate on the new set you are building.


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