A few years back we messed with a M1 vs air gap on a 365 cid flat tappet 10.5 1 mud motor that had ported J heads , we ended up with the air gap and a larger carb 850 than the 750 we ran on the M1, the air gap made better power thru the rpm band, the cam stopped @ just over 6500 so the M1 had no advantage up top