DrewG

Hi all,

I just installed secondary cat bypass pipes on my wife's GTS. The sound increase is nice. It sounds a bit raspier, especially in sport mode, but we have encountered a sound that I am having a hell of a time pin pointing. There are no strange sounds or rattles until the car is warmed up, and even then it is at a very specific rpm. I am posting a video, where the vibration can be heard.
It is most audible at the end of the video. The vibration happens almost exactly at the 2000 rpm mark, either under acceleration, or when coasting in gear. I have not reinstalled the stock secondary cats to see if that makes a difference, mostly because almost all of the stock cat bolts were brittle and sheared off during removal, and I still need to press those bolts out. I originally thought that I hadn't tightened everything all the way, but I have been under the car 5-6 times now checking all bolts on the exhaust and the engine under tray. I don't know if this could be a primary cat making this noise, but am looking for any ideas that folks on here may have.

Thanks,

Drew

L_perm

It's the sound of demons from the special place in hell reserved for people who remove their cats.

Or, maybe it's the collective groan from the innocent victims who are forced to smell your truck.

Classy.

DrewG

Thanks for the helpful reply. This issue is now solved. The driver's side exhaust hanger was about 1mm from the transmission crossmember, although not visible from below. It took feeling around to find the tight gap. I bent the hanger away from the crossmember slightly and the sound is gone.

v10rick

This is the first interior sound clip that I have heard from a GTS with bypass pipes. Thanks for posting! Was this in the sport mode? Did you install commercially made pipes?

Nice sound but its a bit loud for me.Curious if your wife is good with this after a few weeks.

DrewG

Hi v10rick,

This video was shot in sport mode. I would say that with sport mode turned off and the cat bypass pipes installed, it sounds very much like sport mode normally does, although with more rasp. It feels to me like the throttle response is slightly better, but that could easily be my imagination. The bypass pipes were made by fabspeed. The quality of the pipes and hardware is very nice, and the fit was good. I also got their sport exhaust setup for my 964 and am happy with that product as well.

As for how my wife feels about them, I'm not sure she cares much. I was the one that was pushing for them, and she kind of goes with the flow when it comes to car related projects and purchases. She's just happy to not have the annoying vibration. I did tell her that it was pretty easy to reverse if she grew tired of it, so we shall see what she ends up thinking of them.

I see that you also have a manual gts, although you have an '09. I kind of wish we had gotten an '09 due to the improved sat/nav/audio system. How many miles do you have on yours?

Drew

v10rick

Drew this is exactly the info I was searching for

The You tube clips are mostly drive by. The exhaust note outside does not matter to me or my neighbors.

Noticed the manual shifts...kinda surprised that your wife is okay with a M/T and modified exhaust.

My GTS is set up so just the exhaust is in sport mode 100% of the time. Some days it sounds too loud and other days not so much.

Purchased my GTS in Dec 2015, presently with 55K mi. Don't know about the audio updates, this has the base radio. Thinking of updating in the future.

DrewG

Rick,

There must be a ton of sound deadening in these things, because even in sport mode with the bypass pipes, it isn't obnoxious inside the car. Once we get back into our neighborhood, we just pop it out of sport mode, and it sounds like any stock V8 car.

My wife has been sold on manual cars since we started dating, and I doubt we will ever get an automatic car. We sought out this particular car, knowing it was pretty much the only manual premium SUV/wagon. The alternatives were a CTS-V Wagon, or an S4 Avant, but the CTS-Vs are rarer than hen's teeth, and the V8 S4s had a lot of expensive issues crop up in the timing chain department.

Once you have driven a manual as a daily driver, the little things that autoboxes do start to get really annoying, i.e. rolling forward when you take your foot off the brake, waiting for downshifts, rarely being in the correct gear for the type of driving you want to do. None of this is even to mention the monotony of driving an automatic.

We got ours about a year ago with 46k and are at ~57k now. It has been a great car with very few issues beyond basic maintenance.

Thanks for the comments.

Drew

L_perm

Sorry for the rant, but I really have an issue with cat removal. We have enough kids with asthma in this world without making it even harder for them to breathe in the quest for a different exhaust note. I just can't think of a reason why a street car should have its cats removed.

I have aftermarket exhausts on two of my Porsches, but both of them have the highest-quality cats available. Interestingly, my 2013 GTS is the one I've left alone.

User 4221

I'm sure you are aware but the Cayenne has four converters. Two primary mounted near the engine and two secondary mounted about 24" downstream.
The primary cats are monitored by O2 sensors and the secondary cats are not.

The secondary cats are used to provide some additional scavenging and exhaust note tuning. If they were critical to exhaust cleanup, they would be monitored by O2 sensors.

Removing the secondary cats will only change the exhaust note, not the emissions level.

No kittens, puppies or goldfish were harmed by DrewG removing his secondary cats.

Andy E.

Scott, you forgot to include trees as well.

Truthfully, everybody on this forum is guilty of contributing to the pollution of our planet's atmosphere by simply driving these gas guzzling hunks. I'm confident that forward-thinking hybrid technology will help curb this issue. If only we can figure out what to do with all the spent batteries....

User 4221

The most ecologically friendly thing any of us can do is to reduce the carbon footprint of one's car by doing the following:

A) Buy the most fuel-efficient car you can afford
B) Keep that car in good repair
C) Own the car for 10+ years

The automakers wouldn't like this but demand would drop and production would drop. Pollution contribution would be reduced throughout the entire supply chain and landfills wouldn't be filled with auto parts and other auto-related items. Recycling would also be greatly reduced.

Once you take into account the entire supply chain, the car's contribution is very small.

luvmy356

Drew, I was looking at the same cars for the same reasons as you before settling on my 6MT GTS. BTW, my resonated bypass doesn't seem as loud so I plan to record a video for comparison.

DrewG

Who makes a resonated bypass? Did you have a chance to make a video comparison?