The Billy Boat Performance Exhaust PRT after-cat system employs exhaust technology unique to the aftermarket So unique, in fact, it doesn’t use a muffler at all. The Billy Boat Performance Exhaust PRT system is simple in design, though more complex in theory, which suggests that you can have a mellow sound at cruising speeds and a sport note when you’re tearing up the streets. It allows true straight through exhaust passage under aggressive driving conditions.