Dbeck002

What is the MAXIMUM compression I can have with plain 87 octane gas. Assuming I have all the timing and ignition mods so I don't have to use that expensive 93 sh-t. [&:]

bobby

why are u worried about higher compression, just wondering[&:]

Dbeck002

When replacing stock heads with ones that have smaller combustion chambers, the compression goes up. I'm looking at about 9.5-9.7, just wondering if that can be ran with 87 octane.

bobby

ummm.... i dont think so man, u might need to use 89 or 93, sorry i cant be of more help

Dbeck002

sh-t. Oh well.

92BOOSTED

Provided you are at 9.5-9.7to1 comp,you can still use 87 if you back your timing down just a little.
If your worried about the price of gas,why are you building this car?Just asking.


Rye

Dbeck002

I am not paying for it.

mdvaldosta

I'd say anywhere from the stock 10* to 12*, often times older engines (like 5.0's) over time get carbon buildup in the combustion chamber - raising the effective compression ratio requiring higher octane fuel - so you see even with stock timing some people may need 89 octane.

Really the key is to run as much ignition timing as you can with the fuel you use without getting detonation, so you need to experiment for the best setting with your car.