I looked up what I get with a 7x5 MAS, MACs pipe, and my own header, which is right around 4 inches, 15% fuel, and that CVA .15 puts out 23,000 rpm. I did a construction thread about it over in the 1/2A forum titled, "LIL DUST STREAK" a couple of months ago. The engine is on a 2/3 size DIAMOND DUST that weighs 29 ozs RTF, and it's about 2/3rds as impressive as my .32 powered DUST
.
Did you shorten the header to the point where you started to see no increase in RPM? If you don't take it that far, then you aren't tuned yet.