Cobra Powr-Flo 2:1 Exhaust System951766888 Product Description If there's one thing Cobra learned about the new Milwaukee Eight engine, it's that it really likes a large 2 into 1 style collector The muffler section uses a PowrFlo 4. 5 inch shell, packed with a sealed pillow of sound absorbing material which provides a deep rumble Features a massive 2. 5 inch collector, which allows for big horsepower and torque figures, especially when changing out the cam for something a little more