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91 octane
Posted: May 02, 2007 5:19 PM
by turbodan
Roughly how much boost can a guy expect to get away with using 91 octane fuel? Thats the best I an get up here at altitude, and I can only do 12 psi without 4.8 to 5k detonation. Its an 8.8 to 1 static CR. I should have gone lower, but I'm stuck with it for now. Is it octane booster time?
Posted: May 02, 2007 5:40 PM
by Duke
Water/alcohol injection time.
Or pay out continuously for octane booster.
Re: 91 octane
Posted: May 02, 2007 5:56 PM
by T_C_D
turbodan wrote:Roughly how much boost can a guy expect to get away with using 91 octane fuel? Thats the best I an get up here at altitude, and I can only do 12 psi without 4.8 to 5k detonation. Its an 8.8 to 1 static CR. I should have gone lower, but I'm stuck with it for now. Is it octane booster time?
You need to retard the timing. That is peak cylinder pressure for that engine.
Posted: May 02, 2007 6:00 PM
by 90e34535i
You could retard the timing a little, or a go a little extra rich. I havent been up to high elevations, but I can run 15psi on 91 oct with 9:1 compression with conversative timing with no detonation.
Water injection is a good call too, or if you can get Xylene for cheap at a Paint supply store it isnt too cheap as an octane booster.
Posted: May 02, 2007 6:01 PM
by M635CSi
What is the intake air temperature and A/F ratio when it starts to detonate?
Posted: May 02, 2007 6:40 PM
by turbodan
M635CSi wrote:What is the intake air temperature and A/F ratio when it starts to detonate?
Golly, I wish I knew. I'm still tuning this one by ear.
Re: 91 octane
Posted: May 02, 2007 6:47 PM
by turbodan
T_C_D wrote:turbodan wrote:Roughly how much boost can a guy expect to get away with using 91 octane fuel? Thats the best I an get up here at altitude, and I can only do 12 psi without 4.8 to 5k detonation. Its an 8.8 to 1 static CR. I should have gone lower, but I'm stuck with it for now. Is it octane booster time?
You need to retard the timing. That is peak cylinder pressure for that engine.
That might have something to do with it. I can't speak for the timing on the homemade ebay turbo chip. If only there was a chip I could buy from a more reputable, experienced supplier...
Posted: May 02, 2007 7:06 PM
by RDAvena
I have 9.0 to 1 compression with 8lbs of boost using 85 octane at 7100 feet and mine does not ping.
FMU and the MS help out a lot though.
Posted: May 02, 2007 11:05 PM
by turbodan
RDAvena wrote:I have 9.0 to 1 compression with 8lbs of boost using 85 octane at 7100 feet and mine does not ping.
FMU and the MS help out a lot though.
I'm using a Cartech 2025. No MS though. Still working around motronic. Theres no reason it can't work, but it hasn't been easy so far. I could do 8 psi with the stock chip without detonation, back when I was content with that. Its too easy to turn it up with a MBC. You get a taste of 15 psi and you realize how great it would be if it could run like that all the time. Its madness.