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pitsen3 10-30-2002 01:50 PM

compression ratio vs octane
I have a 350 SBC and I plan to use a cam with 218/218 duration at .050 and .450 lift. How high of a compression ratio can I run using 91-92 octane fuel?

wrenchturner 10-30-2002 03:29 PM

not over 10 to 1 and that might be pushing it just my opinion (Wrenchturner) :)

bullheimer 10-30-2002 03:37 PM

Boo! same here :eek:

78 monte 10-30-2002 09:30 PM

I wouldn't push over 9.5:1.The motor I'm pullin this winter won't evan run on the new 93 octane gas at 9.53:1. They did some crap to the gas in the last couple years(something like oxigenated???) for the "O-zone"horse ****,now you can't run anything with out retarding the timing.Allthough if your cam is the Crane cam I think it is,it has 106 Lobe sep so It might run better with compression.

pitsen3 10-31-2002 05:16 AM

I had planed on using the crane.

Ted655 10-31-2002 05:36 AM

Since octane numbers are just a way to keep track of the temperature at which gas will or will not pre-ignite AND compression is just one of a few things that determine pre-ignition, you have to make up your own formula. Ambient temperatures, seasonal fuel mix, engine cooling abilitys, loads. speed, terrain, and GVW can all affect pre-ignition.
Yes...Oxy-fuel is spreading thru the country and is "crappy", low mileage, low power gas and will affect engine power and cooling ability. It will lead to early pre-ignition.
I'd try to talk to people who are already using that octane and try to match my driving conditions and compression to theirs.

pitsen3 11-01-2002 05:17 AM

How about a comp 268H (218/218 duration at .050 and .485 lift with 110 lobe separation).
I want good ignition but i do not want to do things like retard the spark because I am over compressed.

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