What is the highest compression ration you can get on pump gas? what about with a little octane boost? 91z28 305 thanx

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1991 Z28 305 1LE, TES headers, 3 Chamber flowmaster, Hi-reving cam... the usual street racer

 

why first of all? but.. it depends, got aluminum heads? i think if you do u can run about another point of compression.. cold air induction might have an effect, i know that intercoolers on superchargers sure do.. trying to get more power or what? i wouldnt go over , well, for the street and if you arent going to SC it, 11.0:1, but, i dont see any big advantage

 

Thats kind of a loaded question. It depends on the cam profile as well. And heads. You could run 10.5:1 with iron heads or 11.5:1 with aluminum heads on pump gas, but that is really pushing your luck and you better have the combo setup just right. I would advise 9.5:1 for iron heads and 10.5:1 for aluminum heads as a max. Another thing is compression really isnt the way to try and pick up some power. I would port match, polish, free up the exhaust, cam, rockers, chip, intake, that sorta thing. Compression is so touchy and can do so much damage it isnt something to play with too much.

 

Its iron head, 305 with a 212/218 .487/.495 comp cam. I want to know because people say that compression=torque. what all could it damage?

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1991 Z28 305 1LE, TES headers, 3 Chamber flowmaster, Hi-reving cam... the usual street racer

[This message has been edited by BenDoe (edited January 31, 2001).]

 

A tree-o-five with that cam... Well I'd stay under 10:1. I think its 1hp for each .1 in compression, not much. What can happen is detonation, and that can either empty your wallet by demanding high octane fuel, or worse yet it can destroy the pistons. Ive seen it happen, and its not a pretty sight. Ive seen valves taken out from it too, but thats much less common. I'd rather pick up some hp elsewhere rather than pushing my luck with compression.