Question about the hiss/rattle after installing HFC's
 

So I installed Berk Tech HFC's and Nismo exhuast Friday night. Love the sound, nice and deep down low, mildly agressive mid range and higher. Overall I'm very happy with the combo, but I have one issue.

When revving the motor while sitting still (neutral, no engine load) as the RPMs fall back down there is a rattle or hiss @ 2500. It's nearly identical to most other YouTube videos I've seen of G37s, etc. While checking it out myself here's what I noticed. There is no audible rasp or rattle from the exhaust note itself (standing behind the muffler). The hiss seems to originate from either the HFC's themselves (inside), or the vibration of the flex pipes of the exhaust.

It doesn't do it while driving (unless it's cool and not fully warmed up), it's only while there is no load and the RPM's are falling. When I was under the car I had my wife rev it up and visibly the rattle or hiss looks like excessive vibration in the flex pipes. Maybe I'm wrong. Any suggestions?

Sound is exactly as seen in this video:

YouTube - nismo 350z berk HFC

I think others have commented before that it's the HFCs that cause the hiss. It kinda makes sense, it's the air flowing through all those little passageways. You hear it on the decel side usually, probably because the pressure is backing off and the sound level of the rest of the exhaust is lower, allowing it to be heard better.

Mine hisses and has a metallic ringing sound on the rpm decels as well.. it's normal, I hear it on a lot of VQ37s with high flow cats. I'm not sure if the sound is there with test pipes though?

What about wrapping the HFC in thermal wrap? I dont have my HFC yet but thought this may help with containing the exhaust noises and heat within the cat. The flex portion of the pipe shouldn't release any additional exhaust gasses or sound as they are a series of rings coupled together that can bend in a snake fashion covered with the mesh braided exterior.

Just suggesting on a whim

Nick

Yeah, I thought about wrapping mine too, I read through a lot of articles and it seams to be mixed opinions 50/50 about this. Some say it will wear out or cause damage to the cats because they are getting too hot and not allowed to breath normally, which could cause them to wear out prematurely. I think even Berk does not recommend doing it. I'm still on the fence about this one.

This is a common sound that has been associated dating back to the 2003 VQDE 350Z!

I have heard it more so than not. In my personal opinion it has nothing to do with the flex joints. None of our systems have ever had flex joints. There have been many speculative conclusions and my personal assessment is that it is the exhaust pulsating through the thinner wall aftermarket cats and exhaust systems. The more back pressure you relieve the louder it gets. Ex. we notice it to be more prominent with resonated test pipes than high flow cats. We hear it very little with stock cats and our cat back.

To chalk it up, it has more to do with the way the engines in these specific cars are constructed and the less to do with the type of exhaust system you put on it. Yes, thicker wall tubing will help it dissipate because less of the harmonics will make its way through so naturally you will hear less.

Lastly, out of all the production exhaust systems we manufacture this engine- VQDE, VQHR are the only cars we have ever heard it in!

I hope that this may help somewhat,

Tony

Yes, do not wrap your cats in header heat wrap. You will trap too much heat in them and possibly cook them.

The wrap is most commonly used for headers to keep the heat in them and not cooking other components on the car that are in close proximity.

What it also does is keep the exhaust velocity up by keeping the inside of the header hot. This works incredible in a turbocharged application due to the fact that turbos are driven off of heat.

okay, just played around a bit more and the sound is definately more prominent in the flex joints, but I agree with Tony that it is not the flex pipe themselves... its simply where the sound most easily escapes due to the construction.

I hear the sound generating in the cat and in the pipe directly below the cat, and this hiss/rattle then eminates most from the flex pipes in the Y. again, the sound doesn't make it to the muffler because I stick my ear right next to the tips of the exhaust and it is just the nice, deep "normal" exhaust without the hiss.

so I wonder, what would happen if a second set of resonators were added (in place of the flex joints). just a thought. I'm not going down that path personally, just ponerding. :p

Fast Intentions had great results with only their catback (on stock cats). Impressive dynos, and a BEAUTIFUL sound from the video. I am STRONGLY considering reinstalling the OEM cats and just enjoying the sound of the F.I. catback exhaust.

How was the fitment on those Berk's with the Nismo exhaust? Plenty of clearance between the heatshields?

Yea no problems with fitment at all, Berks fit exactly like stock. Nismo exhaust bolted right to them without any adjustments needed anywhere and has more clearance than stock in relation to the heatshields on the car, as the Berk and Nismo exhaust don't have the additional shielding that is welded to the OEM exhaust pieces.

Let's get you signed up!!!

Not to beat a long dead horse, but I've noticed this hiss more prominently since installing my CBE. I first noticed it when I did my muffler delete. Then after switching to the full CBE it just continued. Of note, I'm using stock cats so the drop in back pressure with aftermarket accessories in general must magnify the sound.

Interestingly, I also notice the hiss when engine braking. For example, going down a parking garage ramp in 1st gear allowing the engine to slow the car...constant hiss sound identical to the deceleration hiss. The sound goes away if you give a little throttle or the revs drop low enough.

I initially thought there might be a leak, but when I had it up on the dyno, I stood underneath the car to listen and see if i could hear/feel a leak, none to report. Kinda sounds like a brake pad rubbing a rotor doesnt it? I notice it more when I'm in a walled in area like a parking garage, or between buildings.

ive been told its just the way the engine sounds as it de-revs in the 2k to 3k range something with harmonics. i could be wrong but thats what ive heard

if you dont put high flow cats or test pipes you wont get that hiss. its the only way to not have it. a resonated test pipe helps but the hiss is still there