i don't think it's a leak as i've checked all the clamps pretty thoroughly. leaving the car in gear, on deceleration between 2000-3500 rpms, I hear a hissing sound. when i give it gas and accelerate, it's gone. it's a very subtle hiss, but drives me crazy whenever i slow down to hear this noise. thx in advance for advice and help.

 

I have it too.

I think it's the Borla pre-mufflers since if you listen under the car, that's where the sound comes from.

 

Yes I have the same problem. Do you have any ideas how to fix this.

 

here's the fix, at least on my car. I installed the borla dual exhaust today. When I reved the engine and the rpms came back down you could hear a sound best described as a flutter.

We put it back up on the lift and reved again with it on the lift. The sound was coming from the second set of pipes closest to the cats. These two pipes connect to each other in the middle of the pipe.

The fix was to loosen the clamp then using a huge pair of pliers we squeezed the two pipes together at their connection point as much as possible then re-tightened the clamp. This also helped all the other links fit together better. Make sure you tightened up the other clamps a little after doing this.

No more down rev flutter sound.

I hope I explained it well enough and hope it works for everyone.

Doug

 

Thanks Cinergi1 I will try to do the same thing.

 

Hmnnnn that's strange cause that's usually the fix for the hissing, not the downrev. I already put exhaust band-aid over the H-Pipe joint. So my hissing went away, but I still have the downrev flutter.

 

Weird, I know we had the 3rd set of pipes from the end of the car (sorry I don't know the exact names of these pipes) flipped. We moved the right to the left and the left to the right and everything fit together better. I really wish borla would label these two pipes so that you know which side of the car they belong on. As it is you have to experiment to get it right.

Maybe this has something to do with it. My exhaust know sounds like the stock exhaust just somewhat louder. I like it so far.

Doug

 

The noise is at the h pipe at the equalizer tube, just take a strap
clamp and pull the equalizer pipe together and tighten the
clamp down.

 

i think you are confusing the hissing noise with the downrev flutter.

 

I had the down rev flutter but I don't have a hissing noise unless it is coming from the nismo intake. Consider using muffler seam and exhaust tape on all the connections. I did that when I fixed the flutter. I noticed the connections were blowing out a little water from the condensation that occurs inside the pipes. That is a good sign of a leak. There were all kinds of small leaks in the borla exhaust. I think that might solve the problem.

 

I'm gonan try that.....putting exhaust band-aid on all the joints.

 

What do you guys mean by down-rev flutter? If what you are talking about is backfiring (sounds like a series of pops coming down the RPM band) then that is natural for all cars. It is caused by the injectors taking some time to close up and injecting a slightly rich mixture which completes combustion coming down the hot exhaust pipes. This cannot be fixed by the exhaust system, but conceivably by a FMU or maybe some aftermarket injectors.

 

No its not backfiring, there is some back type of back pressure that occurs. It is definitely the H pipe. It doesn't seem to have any bad effects other that being annoying.

 

i think that's exactly what the problem is. some type of back pressure or down rev flutter. if i'm coasting in neutral, there's no sound. only when i'm in gear and slowing down. if it's not bad other than being just annoying, i can live with it. thanks for all the help guys. so there's no cure? it's just the back pressure and resonations of air going through the borla and test pipes then?

 

The down rev flutter is definitely fixable. When I had the noise I put it on the lift and moved the clamp over, you could actually see the hole in between the two pipes. The clamp covered it, but they don't tighten enough to stop the leak. The other minor leaks didn't make any noise it just annoyed me that they were there so I sealed them. to make a long story short the down rev flutter (aka the annoying hissing noise when the rpms are dropping) is definitely from the h pipe not being pulled together properly.

 

I have not heard this... But... Pipes do have a resonant frequency... When sound travels through it and it is at that resonant frequency then you will get rattle or the volume become louder.

Maybe find the point on the piping that resonates the most and dampin it with something like a clamp like a Cello player would to keep the strings below the bridge to sound.

:looks around:

 

Sounds really technical, but my z is not making noises anymore, the noise we are referring to is an exhaust leak. Once the leak is fixed the exhaust pretty much sounds like stock with no annoying resonance. The noise that we are referring to sounds more like a hiss, kinda like the noise a cold air intake makes as it gulps air.

 

As I said before I havent heard this problem with my own ears.

Maybe it has something to do with no back pressure at all from the straight pipe's and true dual set up.

Atleast with an exhaust like the nismo, even though it goes to a single pipe the diamater of the single pipe is larger then the single pipes on the Y pipe. The exhaust gasses meeting in the middle add some pressure.

but with the true dual set up, you have a burst of air out of the left pipe then nothing while the right pipe gives out a burst of air and again and again. so rather then a constant stream of air moving through the exhaust pipe it comes out in burst's.

Stand behind the car and put one hand infront of each exhaust tip and you will feel it on your hands (car must be running of course).

maybe that has something to do with it. kind of like a blowing over a 2 litre bottle of coke effect going on?

See what I mean? It could just be the natrual response.

 

i took my car to an exhaust shop to have them check it out. i told them to check out the H-pipe. they said it was fine, and that if i had a leak, i'd hear it on acceleration, not deceleration. they can't seem to pinpoint the problem either.

 

Initially my pipes under the passenger side were hitting the sway bar; after readjustment I still get a rattling sound below 2000 RMP. Going under again, I noticed that the exhaust hanger is slightly different from other Borla hangers; in my case the rubber connecting the metal hangers were much closer than others I have seen, and make contact when the pipes vibrate below 2000 RPM; making a tapping sound.

I am going to try and insulate the 2 metal rods that are hitting each other and see if the knocking will disappear. It really sounds silly when at idle at a stop; and starting off in 1st & 2nd.



Any other possible causes.

Thanks
Gerald