ORIGINAL: wcmorrison
Not much, about 3%. I suspect 33% is a bit more expensive. I would not expect a great deal of difference in performance. Maybe run a bit cooler.
Chip
Not a real boost in performance, however way too much nitro for an aircraft engine. More suited to a car engine, with an extra head shim.
Also - the more nitro the more heat is produced. The methanol content has a lot to do with how hot or cold an engine runs at optimum mixtures. Nitro adds fuel to the flame creating more heat and the need for a richer mixture and thus lowering fuel economy.
In a car engine not being raced, 20% nitro is all you need. The performance between 20% and 30% is not going to be dramatic. Not to mention the price of 20% is around $32 and 30% is $38-$40 around me - thats expensive!