Is the Tomei supposed to hiss?
 

Hey guys, recently purchased a Full Tomei exhaust with the Tomei y pipe and had a shop install it since I don’t really have any tool. Fitment seems good and everything but I do have a weird hissing sound mostly on deceleration. I thought that normally you only get the “hiss” with test pipes. My cats are stock with just a Tomei, is this normal?

That's just the sound of the motor. Completely normal. If you think it's bad now, wait until you get test pipes.

Embrace the hiss. It makes the Z different. :tup: It really confuses other people on what's going on. :tup:

I have a theory that the hissing is caused by vibration of the exhaust piping when you hit a certain frequency. The hissing gets louder as you change out exhaust components, not because you are freeing up exhaust flow, but because you are changing to piping that vibrates more freely.

You could test this theory by jacking the car up and clamping some heavy weight to the most exposed section of the exhaust.

I can confirm my Tomei hisses on deceleration as well, full exhaust + y-pipe and test pipes. I've heard that the only way to reduce this to a minimum is by running the Motordyne ART pipes instead or by running cats.

There is a couple of old threads on the hiss. The throttle blades go wide open just off idle. The speed is controlled by inlet valve lift and injector dwell time. The hiss comes from the throttle blades being open and no fuel being injected. Creating vacuum being pulled through the throttle bodies. That's what I read any way.