Max Compression on Pump Gas

J.A.B · Sep 11, 2009

Since I have decided to ditch the propane in favor of the Mass-Flow EFI system I have a new issue. I built this motor to run on propane so I ended up with a little over 11:1 compression - now I do have a cam with pretty wild duration ( 283/303 ) so it may bleed off a little. My concern now is can I get away with say 11.3:1 compression on 93 octane without detonation issues - may need to add a littel octane boost but am a littel worried.

Chime in here motor gurus....

midsouthfab · Sep 11, 2009

If you have aluminum heads and keep the timing in check, you should be OK. Just hit a couple of times prettty hard and check the plugs to see what they are saying. You won't be able to run as much timing or you will rattle it(ie. detination)

gomer pyle · Sep 11, 2009

i was always told 10.5 was max for pump gas
my motor is 11.2 and i am going to mix 50/50, if i can ever afford fuel injection
i also run 38 degrees of timing
just my 2 cents, i am no motor guru by any means

J.A.B · Sep 11, 2009

Well if I do have some detonation issue would octane boost be enough to cure the problem? :dunno:

midsouthfab · Sep 11, 2009

on 93 octane just pull 2 degrees at a time out and read your plugs and they will tell you when its not detonating if you cant hear it? I would say you would be safe at around 32 to 34 degrees with that much compression. If you figure how much fuel you actually buy throughout the year riding you proabably wont spend that much more in race fuel in the 100 to 110 octane range anyway. Then your worries are over :driving:

CHASMAN9 · Sep 11, 2009

I am probably all wrong here, but i new a guy who ran a Holley water injection system that misted water in with the fuel to help with detonation. I might have it backwards though. Anybody ever heard of this system, and does it do what I thought? :dunno:

zukiscott · Sep 13, 2009

YEA IT WORKS DUDE.........SAME WAY YOURE HOT ROD SEEMS TO RUN BETTER AND HAVE MORE POWER WHEN ITS COOL & HUMID OUTSIDE......CAUSE IT DOES :dblthumb:

YOUNG · Sep 13, 2009

11.3 on 93 octane is no problem. Hell, my stock LS2 has 11.1 and I've ran it on 89 without any issues. I've seen some motors in the 12.0 range run on 93 without any issues.

Water/methanol injection is very simple and allows the you to run more boost and more timing.