Hissing from hfc, is it a rumor?
 

Hey everyone:

I have heard rumors that if you replace the hfc, or take out the oem, that you start hearing a "hissing" sound. Is this true?

I have also heard that the problem could potentially be an exhaust leak. If so, would it be possible to put an exhaust gasket?

I say exhaust leak because it seems like there are those chappy flanges on the end of the parts...maybe it could be it. If this is the case, should O just buy my own flange and replace them? (maybe a v-band clamp?)

Sorry for the long post with multiple questions, I just want to find someone who has had experience with this type of problem before I take the plunge.

Well I don't think it's so much a rumor as it is an aspect of our VQ engines. I get the hissing when I let off the gas and the engine is in gear and starts to decellerate. The sound doesn't bother me though, I'm not sure if anything can be done to make that sound quieter if that's what you're looking for, short of keeping stock cats on.

BTW: The sound is not present while accellerating at all.

Do you happen to know what in the engine is causing it? What system is it?

Well i don't know why the engine makes that sounds but yes it does. I have Ark r spec resonated hfc and it's makes the hiss in deceleration. I almost can't even hear it but the more you open up your exhaust the louder it gets. I had a 350hr with headers and straight pipes. The hiss was loud

Honestly I don't but if anyone on here does, please let us know because I've been wondering that myself. Curious what makes the engine have that unique sound, I think it would be cool to know.

Well then when I install my test pipes this week I can expect that hiss to louden also....oh well! :driving::vuvuzela:

Think the hiss is related to the VVEL operation with aftermarket exhaust. The exhaust changed the harmonics within the system and it's not tuned for it.

Perfect! That makes sense...Do you, or anyone else, happen to have a screenshot of the table that controls VVEL?

I have Berk HFCs and CBE and the hiss is definitely there. Does not bother me at all and actually sounds kind of 'exotic'. I tell everyone that it is the "snake" inside ready to pounce on some of those lesser vehicles :D.

Hiss will be present, but from a person who likes to tune their vehicle different noises will be present. It's not a big deal. I run test pipes to a CNT CBE.

VVEL controls are still limited, only certain Uprev Pro tuners have access & then ECUtek claims to control VVEL but you have to go to a tuner (no end user option yet).

IMO' HFC or Downpipes is a must
 

HFC really helps bring out some sound life to the Z. So due down pipes of course, if u can stand the smell. But after installing the Berk HFC using Ramps (no room under the car, barley squeeze under it with stock suspension) & doing it all buy my self (FML). Not to mention having a Cat back exhaust on the car already (have to remove the Y pipe on most aftermarket) I can truly say it was a bitch. No question...A whore like no other. But well worth it when you put her in her place and get it done. Glad that **** is done.:happydance:

Those who are experiencing a hiss with HFCs are experiencing it as a result of their exhaust and HFC pipes not mating. Some members are running a HFC with a 2.25 in outlet and then are running a 2.5" exhaust. Or some are running a 2.5" HFC and then a 2.25" inch exhaust. The variations in piping diameter at the flanges are causing air to seep out and creating a hissing sound.

That's a possibility. BUT, some have complete systems with matching diameters. And they still have it. The stock exhaust has it to some degree. If you look back to 2010 or there abouts. It was brought up then.

I'll be installing HFCs to compliment my Injen exhaust and I'll report back to you. They're both 2.25"

It would be great if you can post it. I am curious to see as well.

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.

Embrace the hiss!. :D It gives the Z character. :tup:

I never noticed a hiss. Granted I'm running 3" AAM true duals so I may not be able to hear it

Yep, you got no hearing left. :icon17:

What else are you running with the AAM 3'' True duals. Im waiting for mine to get here but am just curious of what other members are doing.

I got the Res Test Pipes from AAM as well but I am thinking about going a different route for the TP. Looking into the ARK R Spec. Res TP

Edit** NVM i just saw your sig line. lolz. Have you noticed any issues going from smaller piping to the bigger 3'' true duals?

haven't had an issue with that

Hey I've got the Ark res hfc and muffler delete. I have a tiny hiss but not much. I think the resonator on the pipe helps with it.

Looking to see if it's worth switching.. The ark TP has the helmholtz chamber which is stated to help with pressure.. But is it worth it ?


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It certainly helps Ark separate you from your hard-earned ............

Lol.. This is true!


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