Hi Dave - Randy must be busy, I'll take a crack, and he can correct me...

The whole reason you would upping the nitro in the first place is to supercharge the mixture in the hot thin summer air. Adding head shims would mostly just undo the effect of the nitro you are trying to gain. Nitro and compression are almost (I said almost) synonymous. You could just as well pull a head shim in the summer as add nitro.

The whole idea of tuning with nitro is to have your engine shimmed in a mid-range so that you can use readily available fuels without ever having to take apart your motor. So, for instance, you can run 5% in the fall, 7.5% in the spring and 10% in the dog days of summer. Pre-ignition is just advanced timing, which adding nitro or compression can bring if overdone. Glow plug heat range is the other piece of the puzzle.

Bottom line, trial and error will tell you what you need to know. Bring a few cans of different nitro fuel to the field and mix in your syringe for effect, see what you get.

EricV

Thanks guys for the information. I've got so much catching up to do. Eric see you sunday. Thanks again, Dave