[DannoXYZ]

You can use anything you want that doesn’t cause detonation. I’ve blown up so many engines due to insufficient knock-resistance (and too much boost) that I tend to gravitate towards having large safety margin and to deal with worse-case scenarios of hot ambient air, lean mixtures and too much ignition. This all came together at a 110F day at Thunderhill last year when I was using the +7 degree advance pre-gen ignition box, I actually got some detonation by end of session with coolant boiling over @ 240F. I re-installed radiator fan from that day onwards.

After that, I started using 89-octane with new-gen ignition and 91-octane with pre-gen ignition. There are many guys using 100 or 110 race-gas, but at $12-15/gal, I think they’re wasting money that can go towards go-fast parts. That’s paying for too much of safety margin that’s not needed unless you’re running 13.5:1 pistons.