There is a sweet scoobie STi in my neighbourhood that whenever he gets into boost and lets off it sounds like a gun it echoes so loud when it goes BOOM. Is it just an aggressive tune and the fuel system he is running, etc, or is he on E85 too?

 

Who knows, Could just be his exhaust system

 

Probably his tune. He may have a blow off valve and his tune may not be compensating for the extra fuel so that extra fuel will create a loud pop in the exhaust sometimes.

 

Yeah, it isn't his exhaust. You can tell it is unburnt fuel in the pipe igniting. He definitely is running a bov. It doesn't matter how much into boost he goes it'll fire off when he lets off the throttle. He thinks he's Mr G I think rollin round the hood going boom. Heh. Nice car still.