FI HFC
Stillen cat back
04 g35x

Got my HFC installed about 2 months ago. Sound is ok but when I really get on the gas hard I get a rattle(not rasp) coming from what sounds like the cats. The exhaust shop already had me replace the resonators(thought they might be blown/damaged) and that didnt help. They see no exhaust leak and I have no cel. The sound want there befor ehte hfc also. The install question is the shop put sealant on the gasket from the cat to the headers. Im wondering If this is causing a leak/sound?

Anything else I should check on. The sound is rather embarassing and I didnt expect it with high quality parts.

I tried to take a video but failed I will try again to see if this will help diagnose.

 

Is the sound something like this when I gas my car and get it up in the high rpms and into 2nd gear? I have BERK HFC and its only been on my car for about 5 or so months. I too think it sounds funny but I dont remember if it was like this when i first got it installed.



Sounds something like metal hitting each other..

 

exaclty like a metal hitting metal sound but only for a second until you get past a certain rpm I feel like. Im going to try and get video today.

Maybe unrelated my cel came on today ugh

 

Did sound anything like the video?

 

yes

 

I notice once the car is warmed up though, the sound goes away.

 

I'd take your G back to the muffler shop, have them tighten all flanges and carefully check the exhaust system clearance from the cats back. Other members have had a hissing sound due to poor quality gaskets but it sounds like you have clearance issues at cold idle. Do you have the Stillen real dual cat-back system or their y-pipe back exhaust? (made by Magnaflow)
Gary

 

I have the whole cat back with the y/x pipe. Ill try to have them check the the cat hookup again . Its ounds like most of the rattle is there. Do you guys have sealant on the gaskets from the cat to the headers?

 

The gaskets that came with my HFCs weren't impressive so I bought new OE gaskets from Nissan. I have zero hissing or unwanted noise.
Gary

 

I will try that

 

I have the same problem with my HFC's and HR Y pipe. It's worse when the car is cold. I really don't feel like taking it back to the shop though. The guy at FI told me you are supposed to reuse the stock gaskets on one side. I believe the header to HFC side... but I'm not sure if my shop reused them.

 

Incorrect. ^^ use high temp red RTV silicone on the flange between header and HFC. no gasket. tighten down before it dries. then you are done.

Those are the exact instructions from FI

 

I think that's what my mechanic did, but the FI guy (I think his name was Tony) said that the '05-'06 have a better type of gasket for the cat to header side and to reuse them.

I guess it shouldn't matter? Either way I do have some rasp or rattle, and it annoys me. Other than that they sound great.