I actually emailed the EPA months ago regarding the Bi-MOdal exhausts that are factory fitted to BMW, PORSCHE, AUDI and HSV vehicles. Asking how can thye be legally fitted as OEM, That the porsche has adjustments for the Bi-MOdal inside the cabin and that everything stated within the guidelines states that it can nto be a temporary device.
Unfortunately they never got back to me. I can only assume that it can be legal for the following reasons:
Bi-Modal open or closed passes Noise Tests (If adjustable in cabin)
Bi-Modal is closed upto and above the noise test limit depending on exhaust back pressure and engine requirements and is NON ADJUSTABLE in cabin to pass noise tests
Bazeng has a thread on one i think, can nto remember the manufacturer, But basically, you can get a 3" Bi-Modal piece of exhaust, fit it to yours and run a vaccuum line off it, They it will open with pressure and i think it retains 2.5psi of back pressure at all times?
The better one that Bazeng fitted has a control unit so you can set RPM, VACCUUM and Throttle position to allow it to open. You may have better luck having one of these pass EPA inspection thana Varex. But EPA has to confirm how you can make it legal if its offered standard on many vehicles.