The 4th production run of the new design just came of QC this morning so the entire back order list will be finished today and we will ship them out immediately.

If you were on the waiting list feel free to contact us 661 298-7555 or via email sales@motordyneengineering.com

ART pipes are now live on our website.:tup:

Emailed :)

So if I put my order in today, how long until they ship? Are they actually in stock for those not on any list so far?

We have them in stock now. It depends on how quickly we are able to pack and ship.
I estimate ~2 days to ship.

Tony: someone at Z1 mentioned to me that the hissing sound I am hearing after installing the ART pipes is actually coming from the Y-pipe of my nismo exhaust rather than the ART pipes themselves. Do you know if this is true? What exactly is making this sound? It's not too audible outside of the car, but it drowns out some of the exhaust note between 3-5k rpms. I'm wondering whether this y-pipe is too restrictive or something. Or perhaps it really is just a VQ thing that I need to get used to. Any comments?

I havn't personally heard that combination so its hard for me to say, but if Z1 heard it, they are better qualified to say what it is.

Apparently the hissing is very common on this engine. I'll find out soon enough what the issue is because I have a whole lot of exhaust dyno tuning coming up for the Motordyne exhaust R&D.

I highly doubt it's the Y pipe as everyone has hiss with these VQ's after removing stock cats. I have the HKS dual and theres no Y pipe, but a lot of hiss.

They didn't actually hear it. They are just of the opinion that test pipes sometimes cause the y-pipe to make that hissing noise. I'll be interested to hear your testing results.

For those of you with an aftermarket CBE and ART pipes: do you get a hissing noise under heavy throttle from about 3-5k?

the VQ's have the hiss. Some exhausts make it louder/quieter depending on the design. The reason the ART pipes made it louder is due to the increased flow. But if you did regular test pipes, resonator, HFC you would hear the hiss as well. So yeah unfortunately it is a exhaust thing more than the HFC/TP but the HFC/TP tend to get the blame as most people notice it only after installing those.

I have an aftermarket Y-Pipe exhaust and have very minimal hiss with the ART Pipes. With test pipes the hiss was MUCH louder. Now I barely notice the hiss, but with test pipes it was very noticeable.

It is a product of the VQ, so there isn't really a way around it that I know of. Obviously restrictive cats basically eliminate it because they disrupt the air stream so much. I don't have any personal experience with true dual exhausts but I have a feeling that they could possibly minimize it some, but who knows. I will say that the hiss definitely comes from the Y-Pipe. I have gotten under my car and listened to someone rev it, so I know this is the case. But, if you had a true dual, it could still come from the same area.. so who knows if it's a y-pipe thing or it's just a VQ thing.

^^ 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.