As Rob says, the best pump fuel you can get, with the lowest ethanol content.

AVGAS mix is OK, but straight AVGAS isn't the magic ingredient people think it is. You need the AVGAS jet kit, and the HRC/adjustable ignition to get even close to making use of it, plus a lot of compression.* Most people in our experience go backwards on AVGAS! Add to that it's not always easy (in the UK at least) to get it, and the compression and ignition required to get it to work make the motor totally incompatible with U/L fuel, so it can really ruin your day/weekend if you run out.

My MC21 makes 67rwhp on pump unleaded, StephenRC45's F3 made 74rwhp on pump unleaded. He has finally set it up for AVGAS now (after 20 years!), and found another 1-2hp, but I don't know the exact figure as I've not spoken to him for a long time.

*I strongly advise NOT messing with the NSRs compression. The MC21 and MC28 are already right on the edge of what's acceptable, and often extremely close to detonating as it is. That's why a drop of AVGAS isn't bad, but its slow burn rate really plays havoc with the jetting and timing. It simply isn't worth it in my personal opinion. YMMV

The best thing about AVGAS is it's crank seal and bearing friendly... the NSR's Achilles heel.
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Andy.
NSR-WORLD.COM

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