Ok so people keep asking me WTF are you talking about with the 3inch MSR mod. I take no credit for this. It has been designed my Michael South to have a free flowing 3inch exhaust that is stock quiet.
Basicly you start with a standard STI muffler. Piping size is about 2.25-2.5inches.
You then cut off the piping where it meets the muffler.
Then cut a 3inch hole around the inlet.
Then weld a piece of 3inch pipe 20mm away from the baffle wall and so some is sticking out of the rear of the muffler.
Then weld on you 3inch piping to suit your car.
This sounds like a stock exhaust but has the free flowing capabilities as a regular 3inch muffler. It is tried and tested to have minimal if any power loss. The car this one came off was making 220kw. I cant find and dyno sheets to show this though. Ill add a sound clip when the weather clears up.
Now your probably thinking whats the difference between an STI muffler and WRX muffler. Well the internals and baffles are totlly different.
STI
WRX
STI has much larger free flowing baffles compared to the WRX