highest compression on 91 octane

[W.O.T]

i am really thinking about bumping my compression up. it is at 9.25:1
what would be a good number to shoot for? heres a few details on my motor
468bbc
je forged pistons/crank
merlin rectangular port heads
hydraulic roller cam
tunnel ram 2 750 demon carbs.
spinning a berk bc impeller
any recomendations? i would like to run pump gas with an octane booster or maybe half 110 octane. besides changing pistons what else would i need to do? thanks

[infotraker]

I'm running 91 octane with a setup close to yours. Solid roller, 10.5 to 1 comp. Top rpm 7K. Rev limiter now set at 6500 to be safe.

[Nucking futs]

Im running 10.5
;1 with Iron heads no problem, Just take it easy on the timing and watch the temp.
WOT, you could always just mill the heads to raise your compression. Alot cheaper than pistons, If your not doing a rebuild.

[W.O.T]

Im running 10.5
;1 with Iron heads no problem, Just take it easy on the timing and watch the temp.
WOT, you could always just mill the heads to raise your compression. Alot cheaper than pistons, If your not doing a rebuild.
thanks, i would much rather have the heads milled. the motor has less than a season on it. it would be a shame to ditch the pistons that are in it.

[BOOGEYMAN]

We run 11.6 to 1 on an aluminum headed 540 with 91 and no problems for 3 years.

[W.O.T]

will a high compression starter be needed for 10.5 to 1?

[Nucking futs]

We run 11.6 to 1 on an aluminum headed 540 with 91 and no problems for 3 years.
Are your pitons coated? Just curious. Whos cam you running?

[WannabeRacing]

Sometimes we have to step back and forget what we learned. We learned about compression and pump gas in automobiles. Boats have an unlimited supply of cool water. Keeping the heads and chambers much cooler. That in turn will let more compression without detonation.
Here goes a wild and unsubstantiated guess- so take it for what it is worth. With everything else left constant, I think you could get away with .5-.75:1 more than you could in an automibile just because of water temp. -again, this figure is a guess. Not yet proven-

[Jetaholic]

Then again I see automotive engines all the time coming stock with 9.5:1 compression...my 4.8L 293ci Vortec V8 in my truck has 9.5:1, can run on any grade of gas 87 or better, and it's normal running temp is around 208! Of course, this is obviously a computer controlled fuel injected motor so that probably is what makes this possible...

[BOOGEYMAN]

Are your pitons coated? Just curious. Whos cam you running?
no coating and they are diamond racing pistons with hell fire rings.

[cfm]

A good rule of thumb I've seen is no more than approx 190-200 cranking compression on 92+. So I'd say try to keep no higher than 190psi if you don't do alot of testing before hand. 180psi should be quite safe.

[kojac]

Sometimes we have to step back and forget what we learned. We learned about compression and pump gas in automobiles. Boats have an unlimited supply of cool water. Keeping the heads and chambers much cooler. That in turn will let more compression without detonation.
Here goes a wild and unsubstantiated guess- so take it for what it is worth. With everything else left constant, I think you could get away with .5-.75:1 more than you could in an automibile just because of water temp. -again, this figure is a guess. Not yet proven-
My brother is currently running 12.1 compression in his mantra jet. Using 93 octane? Had the heads off to have a hole in the exhaust welded and was considering using a set of edelbrock heads and after checking the piston numbers with them confirmed it was 12.1
The heads he is using are ported 049 oval port chevy heads. flat tappet cam, 37 degrees timing,Single dominator sitting on an edelbrock victor, turning 5700 to 5900 (dependent on weather). No sign of detonation???
We also figured he got away with it due to cold water.
Haven't checked his gauge compression yet. His last motor had a static compression of 10.4 to 1. ,but cranked 220 lbs on all cylinders on the guage. Ran on 93 octane and it ran for 8 years that way before it ate some springs.???
Kojac