No muffler on my RV-8, just a heat muff for cabin heat. My RV sounds a bit more throaty than GA planes, but doesnít approach obnoxious at all.
The reasons for crossover exhaust is to balance the exhaust pulses into a balanced back pressure and improve how the engine breathes. Some sources claim better power or higher RPM with a fixed pitch prop.
Pic of the setup in my -8 with a Showplanes cowl.
Iím a 320 CA PHX, where are you based? Take care!