Compression ratio for 91 octane

[CHANMADD]

I too have aluminium heads and run 11.5:1 on 91 octane and have for years.I have never had any compression related piston damage.Just make sure the timing is right.
John

[SP01715]

Originally Posted by WildBill1965

93 octane 10.5 427 Roush, I asked about the compression and they said ther were at the edge!

I run 91 in my roush with no problems at all. I do mix in a little F&L 111 sometimes (2 gallons on a full tank), but it runs fine on 91. When I first bought the car I was running straight 111 (thats the only race gas I could get from a pump in my area) because I was afraid of detonation, and the car started running like crap (stumbling over 5000 rpm). The mechanic I use called roush and they said switch back to 91. We did and the problems went away.

I have a friend that runs a 444 CI Chevy in a Pro4 (trophy truck) and he is putting out more than 800 hp with high compression and race gas. It gets me thinking sometimes what my motor would put out with a compression bump and a steady diet of 111...