^^ Interesting.

So I get that the VQ naturally makes this hiss, but I don't understand why it can't be tuned away through exhaust design. I mean, at the end of the day we are just talking about gas going through some pipes and chambers.

But the fact that it comes from the y-pipe is very good to know. I wonder if this means the y-pipe could be engineered somehow, in the same way the ART pipes were engineered, to reduce this type of noise. Luckily, Tony is on it!

Does anyone have experience with test pipes used in conjunction with different aftermarket exhausts? I wonder if some cat backs are better at eliminating the hiss than others.

I'll make hiss elimination a priority during the R&D phase.

I am wondering however if the hiss could be a result of exhaust gas flowing through partially closed exhaust valves.

We'll see.

I'm sure they are. The hiss is probably exhaust gasses bouncing around in the y-pipe. It's weird to me that you hear it under acceleration though. I notice it some when cruising, but only if I'm driving next to a wall that the sound can bounce back off of. If I'm stationary and revving, I only hear the hiss when the RPM's are dropping back down.. Or at least, the hiss is slightly there under cruising or revving, but very pronounced when the RPM's are falling, specifically in a certain range (from about 3500-2000).

I'm not engine/exhaust expert.. so maybe this will help Tony explain where the sound/gas characteristics come from..

If the hiss is not directly caused by flow past partially closed valves, its definitely a form of rasp. Rasp comes in many different characters and volumes.

Some sound like a fart.
Some sound like tinging.
Some sound like a buzzing.
Some sound like a rattle snake.
Some sound like a hiss.
Some can actually sound good where it adds character to the exhaust.

All rasp is caused by standing waves and reflections of shock waves inside the exhaust.

It all depends on the design.

Yeah, I am not getting the rasp-type hiss that aadosx is describing. My hissing sounds like a huge volume of air flowing around a sharp corner or something, and never happens unless I am heavy on the gas pedal. I think it continues up to redline, but the engine and exhaust are so loud by that point that I don't notice the hiss as much. It's quite loud, though.

The only other thing I sometimes hear while not accelerating is a burbling sound between shifts at high rpms. I kinda like that sound, though.

Yeah. I think what you're hearing is just the sound swirling around and/or trying to escape the resonators? That was my guess.. I think I kind of hear what you're talking about but I don't really notice it.

Armonster what Exhuast do you have. What you have I believe is just rasp. Not the hiss people are familiar with on decel around 3-4k

I just installed my ART pipes yesterday after work. My exhaust sounds great. It's not much louder from what it was previously, but it's definitely deeper. Thanks Tony!!!

I've got the OEM nismo exhaust. I don't know whether the hissing is rasp or not, but I'd like to find a way to get rid of it ASAP.

I have the HISSING sound on mine too. It's quite annoying. I'm also curiously about how to reduce or get rid of it.

One thing for sure, it very much depends on the exhaust it is connected to. Different exhaust parts react differently when connected to other parts.

Which exhaust do you have?

Just had them installed at Performance Motorsport. It literally took 20 minutes to get OEM cats out from the moment they popped the hood. The demon bolt aint sh!t for PM. I'm going to make a detailed thread when i get home, but in the meantime my quick impression is its louder than before but not much. The ART Pipes still need to break in so we'll see how they sound in a week.

Power, the top end has tremendously improved it simply hauls. The low end is brighter but i dont notice the torque increase as much as i did in my 350Z probably because it was auto. Regardless ive only driven it about 20 miles and all of it was highway. Detailed thread to come later.

Err...I've developed some crazy *** tin-can rattle from what sounds like the driver side. I know we cut the bolt, I saw them do it. It sounds very metallic, embarrassing, and loud.

Any ideas what this could be? It's a constant metal noise. I've recorded it. Uploading the video now.

Here's the link. WTF is this?

Video - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting

I literally drove the car 25 miles to my girlfriend's, no noise. From there drove another 10 miles home, when I rolled down the windows as I was getting off the highway I heard the noise (it was DEFINITELY) not there before.

Can you get under the car to see what side it is on or what it may be?

I have the Boombop Shop CBE. It's a 2 piece slip in exhaust, no flanges. The exhaust sounds great with the ART Pipes. The hissing is noticeable below 4000 RPM. After 4K RPM its a beautiful sound.

I can try. But with the drop, it makes it much more difficult now.

Although it does sound more like driver's side.

Here is what mine sounds like. Anyone else getting this?

well its def not the ART pipes that make the hiss on their own. was talking with kevin today, he just replaced his Gemini with the CNT racing exhaust and said he noticed the hiss and his gemini never had it. Hes had HFC for a while now.

So the ART pipes/test pipes probably make it noticeable due to the increased flow but its something that needs to be fixed in the exhaust. Hopefully the motordyne exhaust will do that.

If you came from stock cats you won't notice a huge low end TQ improvement.. but you will notice the top end improvement. If you come from test pipes, it will be the opposite: you'll notice a huge low end TQ improvement but not any top end improvement.

The only way to have an exhaust with absolutely no rasp or hiss, from every Z I've ever seen personally, is to use stock cats. It's as simple as that. Sadly, there are trade-offs when it comes to modding.. that's just how it is. For all the power you're gaining you have to give up a little something. The hissing on these things is EXTREMELY minimal compared to test pipes.

This is probably a loose ceramic coating bead that got into your ART Pipe when they were making it. Tony already mentioned this earlier in the thread. Did you not read it? ...

I would try to figure out exactly where the noise is coming from first, then go from there. If it's something inside the ART Pipe, I'm pretty sure Tony will take care of you. GL.

Tony said the new production shouldn't have this issue. Though I've already contacted him and he's ready to provide a replacement immediately if I say so. First I want to eliminate the possibility of it being anything else before I waste his time and before I have him send me a replacement I may not need.

Did you listen to the video? It sounds way too metallic to be a loose particle, if you ask me. It also goes away at above the 3K mark.

It shouldn't but if there are any of the ceramic beads, we will use a polishing method... that doesn't involve ceramic beads.

In any event that would be covered under warranty.

Here is a much better video of the sound. Notice as the idle drops, the sound goes away at the very end.

Video - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting

This thread is great! I can't wait till i can order mine

sounds like something is stuck inside the pipes. -- maybe the gaskets?

obviously your dead bolt came out- yours is less than a year old... i wish mine was that easy but it wasn't :shakes head:

Thats exactly what mine sounds like ....

sounds like something's rattling inside the pipes. but how come the rattle goes away by the end of the video?

That's what I don't understand, either. Damn, NeverBoneStock's response has me pretty concerned now. If the ART Pipes failed, I may have to put the OEM crap back on and waste another $120 for that job. And again another $120 to reinstall them - I refuse to drive the car and have it sound like this.

That'd be pretty unfair to pay all that money assuming the failure is the ART Pipes. I'm hoping for the best on Tuesday, but expecting the worst in all honesty.

You don't need to put your stock cats back on I'll send you a proper part. Just let me know which side its on.

Ok cool. I've replied to the PM. If it turns out to be something loose, I will send the replacement back. Let me know when it ships out, Tony.

Thanks again.

i get a hisssss on deceleration on my nismo with CNT res test pipes. just throwing that in there.

Well Arnold, you really need to get under the car to figure out exactly where the sound is coming from, to be sure.. but luckily Tony is helping you out since I guess not everyone has a race jack and jackstands like I do..

That is exactly what mine sounds like and the sound in my case is definitely coming from inside the pipe (the pipe is not hitting the car or anything). Tony is sending me a replacement as well so I'll keep you updated. It stinks that this is happening to some of us, but I guess that's how first production runs are sometimes.

The reason the sound goes away once you rev it up some is beause the ART Pipes (and exhaust as a whole I would imagine) vibrate at different intensities at different RPM's. Around 2000 RPMs (or a cold start) they vibrate a lot.. so that's why the rattle is worst there.

Alright, thanks for confirming that it sounds identical to your issue.

Thanks for those thoughts. I have to point out, though, that people have already indicated that different exhausts produce varying amounts of hiss with these ART pipes. So while it may never disappear completely, it sounds like there are some setups that are better at eliminating hiss than others.

I am hoping to hear some other cars with ART pipes and aftermarket CBEs. I'm interested to see what Motordyne comes up with on the exhaust front, but whatever it is will probably be too loud for my tastes anyway.

Hi Guys,

We apologize for the rattling issues and we are working hard to correct it. The ceramic coating process requires a pre cleaning process that washes and polishes the pipes in a ceramic bead slurry with soapy water.

We took measures to insure the beads could not get inside the pipes but if they still are, we will find an alternate process.

In any event, Motordyne stands behind its design and quality of workman ship. If there are any problems of any kind, with any of our parts we will take care of you and make it right.

Thank you for your patience,

Tony Colette
Motordyne

I'm getting a new pair of ART Pipes overnighted to my shop.

That's definitely working hard and making it right! Tony, you're still the man. This doesn't change a thing about my perception of Motordyne. Thanks for your help and immediate promptness, man.

This is pretty much it man. The more free flowing the exhaust (true dual being the most, OEM with y-pipe being the least), the less hiss you'll have.. but then obviously the more noise your exhaust will produce (louder). Sucks doesn't it. :p

Hiccups are just part of being the first and greatest. Keep it up man. :tup:

+1 for Tony always delivering