Hissing from hfc, is it a rumor?

Nick M

Kinda surprising info and comments in this thread.

Its not a valvetrain malfunction, its not a vacuum leak, its not the Y pipe, its not mismatched pipe diameters.

The "VQ hiss" found in these cars is hidden in the OEM cats. It is a harmonic resonance in the exhaust pulse (sound). The OEM cats and some aftermarket HFC's hide the 'hiss' on deceleration between 2-3,000rpm.

The hiss does not 'come out' with a simple cat-back system, it only typically appears with you replace the OEM cats with either test pipes, resonated test pipes or HFC's. How noticeable it is, depends upon which product u have, who makes it, if its resonated or not etc.

A cat-back alone, should not reveal the hiss.

I have an AAM s-line catback, it had no hiss.

When I added my Fast Intentions test pipes, i now have the hiss.

Its really not that big of a deal, its a very well known sound these engines make when you remove restriction from the exhaust.

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