Most organized racing in the US runs either the stock mufflers or Nelson/Jett mufflers and are not all that loud. Warbird racing is gaining in popularity and use mainly 4 strokes with open headers. My experience is that fast airplanes and racing flourish where they are permitted and die off where there are a group that creates noise issues. The loudest racing are the giant scale unlimited warbirds. Maybe why we race them off dry lake beds in the desert. I would suggest taking on the challenge of going fast within your clubs noise guidelines. Usually the odd man out never wins.