I have a 2015 Nismo Z and I'm noticing the hiss already and just hit 200 miles it's quiet now but my berks are on their way so I'm sure it will get louder. I'm a little concerned there maybe a vacuum leak somewhere. After you mentioned this it happens around 2k and above as the rpms go back down at idle so this must be exhaust? I just don't want to start modding if it could be an issue the dealership should fix first.

Not to hi jack just keeping up with all the information I can since I've been looking into this as well. I'm looking forward to hearing the Nismo exhaust open up a little bit.

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...

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.

I got the same hiss, I dont mind it, I actually think its pretty badass..

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.

Under the $775 option of the Osiris Tuner from UpRev it says that the parameters supported in the ROM editor include "Cam Phasing for equipped vehicles." Wouldn't this be the option that would allow us to tune the VVEL system? If this issue is really harmonics of the engine at that certain rpm then changing the way air flows through it may solve the issue.

Another question, are most of the users on this forum doing the tuning themselves and if so could someone try this or perhaps changing fueling at that rpm and 0% throttle position? That would change the fueling under decel if Im not mistaken.

There is zero point in trying to tune out a hiss. It just exists. Its the note the motor makes on decel. I just had my car tuned at UPREV and they said it was perfectly normal. No performance loss at all.

Its no different than the Ford 302 motor having a prettier exhaust note than a Chevy 350..

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.

You can't tune it out electronically -- but you can "tune" it out mechanically with the right piping and/or resonator.

Changes in diameter on the Y or H will definitely exacerbate the hiss and rasp or rattle will definitely be more apparent with unresonated TP's or HFC's.

I should also note that the OEM standard exahust pipe has rubber "weights" ("slugs"?) affixed to it (can't recall exact location) that are almost certainly designed as NVH cancelers. The S-tune Nismo (Y) and the OEM Nismo (H) don't seem to have these weights as I recall.

Has anybody tried? It may not be worth it, but now I am just interested in wether
VVEL is actually tunable in uprev. Can someone just confirm that it is a table we can modify in the $775 version?

I have no hiss with my berks hfc inStalled - paired with my AAM competiton exhaust setup - see signature for details- no hiss zero to no drone - but aggressive when you want it to be

I'm so glad someone posted this, I just installed my bark HFC's this week and I got the hiss and I was worried I had a leak cause everything was darn tight up underneath. I didn't really understand how a leak would even create the hiss but I was worried something might have been wrong.

Oh well, maybe some people will be fooled into thinking it's a real quiet blow off valve or something. Z's are exploding with personality already, a hissing exhaust? Just one more unique thing to love about my car. As long as nothing is wrong, I'm happy with it.

Update: I installed Berk Test pipes, along with an ARK exhaust and Injen intakes. There is in fact a hiss after 3500 or 4000 rpm...my friend jokes about it as my "ghetto turbo".

You really don't even notice it. It is just another "race-car" noise, like the whining of the transmission or the shifting after adding solid bearings, etc. You get used to the smell and noise...I suggest getting the HFCs if you are bothered by that smell. The actual process of installing them was fairly straightforward...annoying though.

Is this a problem with fast intentions HFCs and Che?

I have it with my Berk HFC's and Ark cat back, it's just what the engine sounds like when it exhales better than stock. I only get it from about 3500-3000 RPM, anywhere else and I don't hear it at all. Which makes it fun while slowing down and downshifting just to hear it.