GMP Performance

We put a set of Fabspeed's Secondary Cat Bypass Pipes on a Cayenne GTS recently.

Made of T304 high-polished stainless steel, these pipes add 15 hp and save 30 lbs of weight over the stock 4-cat setup. They connect to the factory downpipes and midpipes for a perfect fitment, and include Wurth hardware and copper gaskets. Improvements in power, throttle response, and even fuel economy are some of the benefits, and they will not set off your CEL.

Pics from the install:



Stock secondary cats


Fabspeed Bypass Pipes


Stock secondary cats removed


Connection to stock downpipes



Pipes installed






Let me know if you have any questions!

pdxjim

Nice install. I believe everything except for the HP gain. :-)

GMP - Matthew

How much power did yours make?

Slow Guy

I have them on my '06 "S", like the sound improvement. Bet they would make a really nice sound on a GTS with the sport muffler system.

Toby Pennycuff

Cost? Any impact on factory warranty? (IOW, do I need to bribe my Shop Foreman?) Availability? Got any WAV files of the before and after in Sport mode?

Inquiring minds want to know!

Toby

Basal Skull

are the pipes narrower dia than stock? sort of look like it from the pics...

User 4221

Yes, by about 1/4 inch. The ends are flared to mate up to the factory system.
When compared to the cats, I'm sure they flow better.

On a Gen-1 CS, the pipes give the truck a raspy sound. On a turbo, it sounds much better.

Basal Skull

Is there a technical reason for the smaller dia? seems like a no brainer to keep the same diameter on a performance set up... does the flow need to be similar to stock to prevent CEL? for example

User 4221

Nope, nothing monitors the second set of cats so a CEL is highly unlikely. The only reason I can conjure is the flare mounting may require extra shoulder to accommodate the weld of mating the pipe to the triangular flare.

Or, they went cheep and are using smaller dia. pipe. For the price, I hope it is the former and not the latter.

Give it a few mins and JoeFab will be on here to tell you how great the product is and the HP bump. BTW, I believe the HP bump is a function of cold air intake AND bypasses.

Do a search on Fabspeed post-sale support and then make your decision whether to do business with them or not.

k722070

after a couple months I didn't like the stock exhaust sound on my 08 gts, even with the sport button pressed it was too subdued. but this is utah where trucks are loud...
so I installed the fabspeed cat bypass pipes, the sound is better and its an easy mod.
I still wanted more noise so I called around for a gts exhaust, only fabspeed claimed to have one so I ordered theirs.
in fact it doesn't fit, the gts exhaust is different from the other models. I had to take it to a shop to weld it. with an s or turbo it just bolts in place.
the good-
at idle the sound is especially amazing. extra deep rumble while driving around and under accerleration its great. parking garages and under passes are something to seek out and enjoy.
the fabspeed exhaust is the 'mirror polished stainless steel' and looks great, the tips aren't as nice as stock though.

the bad-all the bad happened with just the bypass pipes
at start up there is a loud rattle and pop as the engine settles.
there is a spot between 3400 rpm and 4000 rpm where the exhaust sounds overwhelmed, before and after are great.

at some point I will put the original cats back on in order to check the start up rattle issue, maybe just the new exhaust will be the perfect sound set up.
overall I highly recommend new exhaust with or without the cat bypass pipes if you want more sound.
on the other hand, this setup is loud and some of your neighbors might get mad if you live in a quiet area. there are a few harleys where I live and I swear my neighbor has straight pipes on his g-wagen so its no big deal for me.

I noticed no seat of the pants power difference, just great sound.

GMP Performance

We don't post our prices directly in forum threads (easier to adjust it only once in the event of a change), but here is a link: http://www.gmpperformance.com/index....ail&PID=105445

Should have no issues with warranty unless your dealer is unusually picky. The car has 4 cats to start with, and you are only bypassing 2. These are in stock and ready to ship as we speak.

I have a video on Youtube here: http://www.youtube.com/watch?v=2ND0xanKP0o

I was hesitant to post because the sound quality is not the best. The microphone on the camera really doesn't convey the depth of the exhaust sound very well (esp the bassier notes). But at least you'll get an idea of the volume increase


The word from Fabspeed is 2 3/4" piping. It's possible that it may be slightly smaller than stock (didn't measure first-hand), but honestly that has almost no bearing whatsoever when you consider the amount of flow that you are opening up. If you've ever seen what catalyst material actually looks like, you'll know what I mean.

pdxjim

I did not expect increase in performance and don't know if it happened. I like the sound with the bypasses. First time in for service after the install, dealer mechanic noted on my order that it was missing the back two cats. Asked service wrtier about that and he said if there were problems that were a result of them being deleted, it could be a problem. That was about 45K miles ago and no probs. Out of warranty now.

Slow Guy

I asked the SA at my dealership if it would be a problem with either the main warranty or the CPO before I ordered them and he said it wouldn't be an issue with them. I got the impression that if they wanted to be ****** about it they could but they don't make an issue over it.

Basal Skull

Hi
It's not that simple, resistance through a tube is related to the diameter to the 4th power...
So, AFAIK, a change from 3" to 2.75" (if Scott C is correct) works out to about a 29% increase in resistance...((3 to power of 4 - 2.75 to power of 4) divided by 3 to power of 4)
and yes I have seen catalyst material, some of the increase in resistance is offset by the increase in cross sectional diameter.