1Jimbo is quite right...a tuned exhaust is by far the best way to go for more power. If you're after the maximum then forget about the so-called pretuned pipes, there's no such thing. For normal flying a wide band pipe is the most suitable because it'll operate over a somewhat larger rev range although not giving quite as much boost. It's also much easier to dial in.

As for the carb mod, you're talking about a ram air scoop like what some high performance cars use. Mainly all they do is pick up cool air from outside the engine bay and we don't have that problem Nearly all carbs nowadays are more than big enough to handle 16-17K revs, in fact they're so large that muffler pressure is needed to help get fuel through.