Thanks for sharing your source material, I Fly... yeah, you did mistate the gasoline octane.Originally Posted by I_FLY_LOW
Your O320 is approved for use with 80 octane avgas... that is 80 Motor Octane Number (MON).
That equates, roughly, to a mogas AKI (pump octane) of 85... so as you know from the EAA and Petersen STCs, you can operate your aircraft on conventional regular mogas, without ethanol, as long as you have the STC and have complied with any conditions (some low wing airplanes need additional fuel pumps, etc)
You were calling that 87... but the 87 in 80/87 is the rich supercharge rating, which operationally doesn't affect your normally aspirated engine. That 87 number comes from an F4 octane engine, and doesn't correlate well to any other octane numbers, like the MON+RON/2 or AKI that you see at the gasoline station... so it's misleading and technically invalid to refer to that number in deciding what fuel you want.
I believe the Piper of the thread title has a Lycoming engine certified on the no-longer-available 91/96 octane (or 91/98 octane) aviation gasoline. The 91 MON, motor octane number, correlates to a mogas octane of 96, which you won't find anyplace but a gasoline station that sells racing fuel. However, Petersen Aviation has an STC for those Lycoming 91 octane engines to run on premium unleaded ethanol-free mogas. I don't recall the minimum octane they specify, but I think it's 93 AKI, pump octane, which brings us back to my original comment... it's difficult to find that stuff ethanol free. It's nearly impossible to find that stuff in the West.
Ignorance isn't bliss when it comes to engine octane numbers. People who just shrug and say, "gasoline is gasoline" can end up off airport in a field somewhere, with a hole burned in a piston.
Paul
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