Hissing from hfc, is it a rumor?

Jordo!

Switching to a larger diameter Y pipe will create a very loud hiss.

Replacing OEM cats with unreasonated HFC's or TP's will result in farty rattle.

Both will be primarily on decel around 2.5 K or so RPM.

Only solution is to go OEM diameter Y (or Nismo OEM H), and resonated HFC/TP or LTH. Other than that its hit or miss to fix. Good luck...

__________________
Enjoy it. Destroy it.

Nick M

None of this is true.

I did not have a hiss when I replaced my OEM y-pipe with my AAM y-pipe and catback.

I did not get a farty rattle when I swapped my OEM cats for FI test pipes.

Resonated test pipes can and will usually hiss just like non-resonated will.

__________________
| 2015 Nismo headlights| 275/305 | Z1 spacers | Eibach Pro-kit |k&n typhoons | AAM S-Line catback + FI test pipes | Stillen splitter |

Jordo!

If the diameter was wider on the Y pipe, it almost certainly hissed.

If your test pipes were resonated, it didn't rattle significantly.

If the AAM Y pipe is about the same diameter as OEM then that's why it didn't hiss.

The cat-back muffler is not the issue -- all the noises are coming from diameter transitions and resonance from everything just past the headers. Whoever optimistically hoped it could be dialed out via VVEL, unfortunately, is mistaken. No one's found a way to do that and it most likely just isn't possible.

__________________
Enjoy it. Destroy it.