Just want to make sure the FGT owners here on the Forum understand and do not misinterpret "octane" for "power". The oil companies over years of implicit advertising have insidiously paralleled to two concepts to the general population. I would hope our FGT constituency is smarter than the general automotive fuel purchasing public and can understand and disassociate the two terms.
Octane in and of itself has nothing to do with BTU (or potential heat energy) content of a fuel. It is only a measure of detonation resistance which becomes more necessary as internal BMEP (brake mean effective pressure) increases due to increased compression ratio or advanced spark timing. Because octane is a measure of detonation resistance, a higher octane fuel actually burns or combusts at a slower rate than a lower octane fuel. This concept does take some thought. It is so convenient to think that filling the fuel tank of your 87/91 octane engine with 93+ octane fuel will get you more power…..but it just will not and you are wasting your money.
FGT tuners get to play with (among other things) the Air/Fuel ratio map, spark advance curve and inlet charge pressure (non-OE pulleys, Wipples, turbochargers) all of which do significantly alter engine power output for a given fuel. And as they play with these variables, to preclude damaging engine detonation, fuel octane requirements do go up. To accurately determine how much octane a fuel must possess to avoid damaging detonation for a given atmospheric condition (which can vary widely as we use our cars in many different temperature conditions) is very complicated and I seriously doubt any tuner has the instrumentation or patience necessary to map the octane requirements over the engine operating band at different temperature conditions. Thus they (to protect your engine and their reputation) conservatively recommend certain minimum octane rated fuels for a given “tune” level. Probably good to heed their advice and run higher octane fuels for more aggressive tunes, but their recommendations may be more than necessary or may not be enough for your particular operation.
