I have a 410" SB with Diamond W2 heads. 3" through the mufflers and 2 1/2" tail pipes. I have Dynomax super turbo 3" mufflers and 2 1/2" Ultra Flows in the tail pipe. It is quiet. Super Turbo's are not enough by themselves. If I had it to do over, I would use 2 1/2" all the way withg hemi super turbos and ultra flows. I also have TTI 1 7/8" primary header pipe. Rectangular port(big) W2's are a bust for a street machine ( no bottom end torque )