351 max compression on 87 octane
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Senior User
Joined: Aug 2010
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From: Port Washington, Wi
351 max compression on 87 octane
just curious what the highest compression ratio would be to run 87? i know there are alot of different varients here but just a ballpark would be good. i would like to use flat top pistons with two valve reliefs. im not sure how well these would work with gt 40 heads. i dont wanna risk having to run premium as this will be in a truck that will most likely be a daily driver. if i cant use flat tops i will order the stock style dished pistons. thanks!
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Joined: Jun 2006
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From: Ottawa, Ontario
This depends upon the actual chamber size on your heads... meaning you should measure them don't just go by what the internet says they should be.
Directly answering your question I think you could get away with upwards of 10:1 but as usual it depends upon everything including the cylinder head chamber design and finish(as cast, smoothed, polished), the cam profile, the weight of the vehicle, the axle gearing, the tire size, etc. My 5.8 has flattops with 4 valve reliefs which is equavelent to a small dish but if I remember correctly it worked out to about 9.2:1 with the cylinder heads I was running at the time(I measured the chambers and piston "dish" volume) and that motor ran quite well on 89 octane fuel which is Regular here in the Great White North.
Directly answering your question I think you could get away with upwards of 10:1 but as usual it depends upon everything including the cylinder head chamber design and finish(as cast, smoothed, polished), the cam profile, the weight of the vehicle, the axle gearing, the tire size, etc. My 5.8 has flattops with 4 valve reliefs which is equavelent to a small dish but if I remember correctly it worked out to about 9.2:1 with the cylinder heads I was running at the time(I measured the chambers and piston "dish" volume) and that motor ran quite well on 89 octane fuel which is Regular here in the Great White North.
Senior User
Joined: Oct 2010
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Conanski has your answer covered .
What you need to know is your static compression which is a little harder to figure out . There are a few internet calculators available . 7.5:1 to 8.5:1 static compression works with todays pump gas .
A cam swap can lose you a point on compression ratio .
What you need to know is your static compression which is a little harder to figure out . There are a few internet calculators available . 7.5:1 to 8.5:1 static compression works with todays pump gas .
A cam swap can lose you a point on compression ratio .
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