Get a set of Dallas Mustang's 'MIL Eliminators' which will keep the "Check Engine" Light off since the Prochamber doesn't have cats. Go here
www.dallasmustang.com for those. The prochamber is no louder than an off-road h-pipe so it won't be too loud with Flowmaster 2-Chambers. It makes pretty good power because it is like an x and an h-pipe in one. I'm not sure about actual RWHP though but I'd guess 8-10 HP at the wheels. I'm thinking of getting one myself but emissions testing is coming up soon. Anyone know how to pass without cats?