MSefi.com read only forum (Jan.15,2018)

Presently I'm tuning for Premium (91 Octane in Colorado) on my Turbo'd project.

Is there some "rule of thumb" or calculation that I can use to estimate how much advance I can gain under boost (more advance = more power) when using a higher octane fuel like E85 (estimated at 105-114 octane) or Race Gas (i.e. 97, 104, or 110 Octane)?

I added 5 deg. advance across the board, except under boost, when I started using E85. This is not a fair example I suppose, since I'd ping without a high octane fuel. You do know that you have to pull advance out when under boost right?

sure do... 1.5 degrees retard per 10kpa (or 1 degree for 1 psi, 10kpa = 1.5psi)

you were able to add 5 degrees advance going from premium to E85? Theoretically you should be able to add almost that much to the Bins above 100kpa too. E85 is a finicky thing, it loves compression, makes it combust better... also will produce more power than gasoline when burned at Stoich.

Yes, my timing under boost is approx. 5 deg. more with E85 than with Av gas. I've never been able to use premium. I'm pulling 1 deg per 1 lb of boost. I run a little more conservatively than I'd like because I don't trust the % of ethanol to gasoline in E85 to be consistent. It can vary from 65% to 80% depending on the time of the year. I plan to start checking my fuel with a hydrometer each time I buy it, (in a 55 gallon drum).