What octane should I run

TT5.9mag said

Interesting, I’d recommend the exact opposite. Start with 112 and get a baseline tune up in it then strip away octane until the power starts to go away, that’ll give you your limit. I’d rather start with too much octane. On the dyno the fuel price is what it is. But you’ll know what your engine wants.

Click to expand...

That is a very valid testing procedure alternative.
MM has MUCH more motor than me, only a 500hp iron head 440, 10.5, and I definitely can run on Cali 91, but since I now have access to AZ avgas, I toss in a couple gallons per tank, cause I can. And avgas in AZ is cheaper than Cali pump 91.
Straight avgas or E85 might be a perfectly good alternative to race gas. Diagnosis time.