Hi all, question for ya.

I recently installed hfc on my Z. 2 of The gaskets got ruined during shipping, so i went to autozone and got oem ones worked fine no leaks.

Now heres the thing. The HFC header end is about 2.25" inside diameter and y pipe end is about 2.5"ID, the stock cat is only about 2" ID at header end and just a tad bigger on y pipe end. The OEM gaskets i bought are made for the smaller OEM diameter pipe meaning they are about 1/4"+, smaller than the HFC inside diameter.

After install, i could feel a slight difference/improvement in mid range power. I also noticed that i have a hissing sound almost like an exhaust leak or little miniature turbo spooling, but only under hard accel. 3/4- WOT. If i drive high rpms and dont smash on the gas i dont get the "hissing" sound, only under hard accel. and only from the passenger side area, and thats the side i used the OEM slightly smaller gaskets on hfc install. So i got under my Z and checked the entire exhaust for leaks w my handy stethoscope and retorqued all the hardware. No leaks found, nothing loose.Ive heard it being common for Z's to develop a hissing type sound after hfc install but it always seems to be reported on decel not hard acceleration.

So my question is this. Are the smaller gaskets hindering performance at all by not allowing the exhaust to flow as easily past the gaskets since they are smaller diameter than the HFC. And also would this be responsible for the hissing sound im getting??

Any insight to this would be greatly appreciated! Thanks in advance guys you rock!

 

Yes, the wrong gaskets will affect your normal performance. Get new gaskets in the correct size and get those in ASAP.

 

Figures, back under the Z :-(
Hope its not a huge problem finding the gaskets i need. Any suggestions? Thanks!

 

You won't have problems finding the gaskets. If the local auto parts store doesn't have them, then you can find them online from someone like http://www.conceptzperformance.com/

The current setup won't mess up the car, but it's not helping either.

 

I doubt the gasket will last very long hanging out in the hot gas flow with no support. It's going to burn away to the ID of the flanges.

 

Thanks, you the man! So whats your take on the hissing? Prob the exhaust struggling to get around the gaskets?

 

Interesting theory. They are the fel pro metal gaskets.
Will they have the same result? Or too thick to "burn off"?