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Old 05-25-2005, 12:46 PM
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comp ratios

Originally Posted by jimbobneutral
I don't know.. My car has 10.1:1 on 91 octane wich is available at all gas stations,and I have no probs with it. My cam is a decent size for street being .49 lift on both intake and exhaust with a 236,230 duration. Runs nice, loud but nice.I forgot, steel heads to.
Im not saying that 9.5:1 is an absolute ceiling, but rather about the upper ends of safe limits with most engines. Most can get away with running 10:1, or even 11:1, with steel heads on 91 or 93octane, however, there are a lot of places in the country where 91 and 93 octane gas just isnt available. Thats why I suggest a compression ratio of 9.5:1, which generally will peform quite well with 89 octane gas. Another factor is that going over 9.5:1 compression usually requires more than flat top pistons, unless you have small chamber heads, and domes add to the cost of the engine, as well as the cost of the higher octane gas. What little there is to be gained in a street engine going 1/2 a ratio higher, to me just isnt worth the added expense, along with maybe having to travel out of your way to get the higher octane fuel. BTW, I have a 351w with twisted wedge heads running a 230/235 degree, .510/.515 lift cam, and I run 9.5:1 compression, on 87 octane, and my engine was dynoed at 398 HP at 5500 RPM. I cant complain.
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