GAS MILEAGE ....

Cylinder pressure is my friend
and rpm is the back-up.
And a manual trans is the enforcer,lol.
If you don't have EFI, then
You gotta get the carb off the mains, and working on the low-speed circuits. Then you make sure every molecule of gas that gets into the chamber, contributes it's fair share, to the production of pressure, and that none moves thru the chamber unburned. piece of cake.

'Course if you have an 700hp monster, 90 might be right. Ima talking 400 or less. Actually that combo went 106 @3650#, so 340hp or so.