Acerbus

I recently had an exhaust shop install a set of ARH headers with a catted xpipe on my car. Ever since I had to change back to stock mufflers (from SLP LM's) but more importantly, I'm noticing a new sound coming from my car.

It is this kind of "hissing" "shooshing" sound coming from under the car. I checked for exhaust leaks and even had the muffler shop take a quick look using soap water on the joints of the exhaust and it's tighter than a space shuttle. I've even started to notice the sound on the youtube videos of people with the same setup. Like this video, for example:
http://www.youtube.com/watch?v=ZUmvX9vqAgY

Notice the "SHOOooooohh... hissssssssssss" coming from under the car when he first starts it and when he revs? I have that exact same sound.

Is it really normal with these headers? Where does it come from? The highflow cats?

It's driving me nuts not knowing. If it's normal then I can just "get used to it" and relax.

KLO

I have the same thing with my headers. They aren't ARH but the entire system is welded so I know there are no leaks and I had a shop look at it. The shop told me it's a tick and hiss from the inside of the header caused by the gases flowing. I got under the car and had someone rev it and I narrowed the sound down to the collector. Maybe it has something to do with all the gases combining?

JMoraru

Im pretty sure that is exactly what i have with my OBX LT headers. i also think it is more distinct with the o/r pipe than the resonated one. i spent HOURS trying to make sure nothing was leaking and all of that(which i did have a leak), but even now it is still there. It doesnt seem like the exhaust is leaking either. Im pretty sure its just a long tube thing?

vasman

I have Kooks headers, and there is some of this hissing noise you describe. I believe it has to do with the gas flow. I have spend a lot of time trying to narrow down the source of the sound and I gave up. I do not have any leaks. The good thing is that I hear it less and less these days.

If you think about it, the manifolds are a thick cast iron collector, while the headers are thin stainless steel, that can emit a lot more noise than the manifolds due to gas flow in them.

My 2cents.

CalmLikeaBomb

I have an O/R H pipe and I have what seems like a leak noise but my shop checked and no leaks. I think its just the way the exhaust resonates in a catless setup

Acerbus

Well, that makes sense. I didn't think about it that way.

Thanks for the replies, guys. I feel a bit more at ease now. That hiss was certainly on of those things nobody warns you about on having LT headers.

I'll be installing a set of Borla's on my car soon, so maybe those will drown out the noise.