I had Fabspeed Bypass Pipes installed on my '09 GTS last weekend.

Overall I'm happy with the results, but I have a couple of issues:

1. On a cold start, they sound like they are rattling for about 3-5 seconds. I verified that the pipes are NOT hitting the transmission cross brace, and they are not hitting anything on the under-carriage of the car. I believe it's pure resonance that I hear coming through the pipes as the warm air from the manifold passes through the cold pipes. It's a very loud and bad sound that I hope goes away over time. Anyone else experiencing this?

2. The pipes sound equally loud in Normal and Sport modes under full hard acceleration. In sport mode, it might be marginally louder....perhaps 5-10% but I'm surprised at how loud they are in normal mode. Not necessarily a bad thing, but something that is noticeable. When cruising with a light throttle there is a big difference in sound pressure levels (SPLs) between normal and sport....as it should be.

3. The sound coming through the pipes is very apparent, and comes on VERY quickly when reaching a specific RPM. I believe it's at around 2,800RPM. It sounds as if a valve opens to really create the higher SPLs. I wish the increase in sound with the throttle was a little more gradual and not so abrupt. It sounds like a switch is being turned on and off. Again, anyone else experiencing this?

Below is my video of the before and after with sport mode turned on and off. I apologize for the poor audio quality coming from my point & shoot camera. I appreciate your feedback.

http://www.youtube.com/watch?v=b4mrZt3N37M

fabspeed makes nice stuff, good luck.

You should try putting something over the mic to reduce the high pitched air sound that drowns out the rumble of the car.

pardon my ignorance , but i didn't know that there would be a difference in engine sounds when switching modes. i thought it was mainly the suspension and shifting charachteristics that changed?

and PSM sesitivity.

Rattle sound on cold start is normal... Mine does the same thing and it does not go away. I have had the pipes for some time now. The rattle should only last a few moments while the engine warms. If you shift it into reverse it stops right away.

on some gts turbo and turbo s you have a seperat sport buton, this one opens a valve on the exhaust system and change setting on ecu ....see pic http://andreas.bloggingon.net/Images...detauglich.jpg

AAAAHHAAAAA,,,, I SEE
thanks

Thank you very much for your feedback.

I have to say I am not happy at all with the rattling sound of the pipes on a cold start. I live in a condo with a common parking garage, and it's embarassing to say the least when someone sees such a nice SUV start up and make a sound like something is wrong with the vehicle.

I've heard others complain about the rattlng noise, but I'm unaware if the problem was ever rectified or has gone away.

I find it hard to believe that this noise is considered normal. What is Fabspeeds recommendation on how to fix this problem?

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I was going to do this upgrade soon, but this thread has got me thinking! I hate that!

Does anyone have any experience with these bypass pipes on a 2003-2006 CS ?

Any comments, good or bad, annoying rattles, leaks, resonance problems.

Also, are the emission levels for CO, NOX & THC exactly the same before and after the bypass pipes are installed.

Any comments on installing bypass pipes on a 04 CS? (good or bad)
Should I leave it stock or not?
It seems fast now, will it make much of a difference?

I am on the fence on this one and need your help please!

well i have them on an 05 CTT and i have no problem what so ever. No rattle at at. I know its not a CS and because of the turbos will not be as loud, but i could not be happier.

I have them on my 06 S. No issues at all with rattling on cold starts here. The sound can be MUCH louder outside than from inside the cabin. It has almost a motorcycle quality to the sound. No change whatsoever in emissions or emissions control systems. The first "cats" are not involved in any way whatsoever with emission control. Overall sound depends a lot on throttle position. At light throttle, even at higher rpms, the sound quality isn't too much different from stock. When you lay into the accelerator, however, it really rips.

I have the rattling noise at coldstart. My dealer has tries to install the pipes twice but the noise remains. I think this is an install issue not a product issue. I will probably go visit Fabspeed in PA to get it done right, have full faith in their products and service.

Pros so far
1) Will not affect emissions whatsoever (I am still a bit skeptical on this one, as one would think that it would be lower with two cats)
2) Better sound (the Cayenne could definitely use this 100%)
3) More power ~17 HP (is this true and can you really feel the difference in the seat of your pants, any 0-60 real #s out there)
4) Better mileage (is it really enough to measure or just more theory)

Cons so far
1) May rattle at startup (would drive me completely insane)
2) May attract Smokey (not a problem, the vehicle does that anyway)
3) May cause possible exhaust problems/leaks due to unsupported tubing (this could be a major problem over time, why don't they have hangers like the cats do)
4) Resale value (not really a con as it can be easily removed for that soccer mom buyer, sorry for being so sexist)

This is why I am still on the fence!