Originally Posted by m4a1mustang

Certain X-pipe configurations cause the hiss. It will be amplified by the addition of HFCs, TPs, or LTHs.

I know with FI's X-pipe, even with stock cats, there's a good bit of hiss on decel in low RPMs. I don't think the H-pipe systems hiss, and I know that the systems without a crossover pipe have no hiss at all. ZCarMan and Tooohip both run HFCs with the AAM V1 CBE (no crossover) and their cars have zero hiss.

Steve, as long as your Berks use an X-pipe crossover you'll probably pick up an audible hiss once you install your HFCs.

Note: I used "hiss" in every sentence of this post.