Y not just get a one-off exhuast made to between 2 1/4 to 2 1/2 inches. IF ur running a stock D16 motor. Others, I have no idea about. But... that what I run and it gave me all the extra power I need.

Mine isnt loud either, nice riciest, its not raspy or any of that. The muffler itself is a Cherry Bomb "Turbo" so it provides enough backpressure for the small motor at high speed. And... u still get ur 40+ mpg on the freeway. Without killing ur ears.