I personally talked to the owner of Maxspeed over the phone who owns a Box S himself with this exhaust intalled. He said that there is little to no resonance at all in the cabin and that with his ECU on the fritz and #3 not firing correctly he was still getting a 25 whp gain. This is the exhaust that I bought. My mechanic works for Penske racing and he said that it looks very well built and thought out, just not that pleasing to the eye.
