Yes they do, but it's not going to be as big on this car as it would on cars where, say, there are cats built into the exhaust manifold.

I would think the bigger you go with the piping, the louder it would be, although it's not going to be a huge difference, especially with the Supersprint which is a pretty quiet exhaust as well. I would think the J's would be the loudest (since it has the biggest piping), but Hytech could definately build you an amazing header whether you get an exhaust from them or not.

If you're really that concerned w/ the test pipe thing, why not just get a T1R test pipe that has flanges on it for the stock cat's heat shield? Then just switch it back out for the cat when you get your smog test. That would seem to be a much cheaper, more reasonable way to go if you only want to make the car a little louder.

 

 

i installed the header after the exhaust. the exhaust sound got quieter than before! but more refined. the engine noise got louder. i was amazed that the header would reduce the exhaust sound. i had a test pipe both before installing the header and after.