Tonger

After deciding not to modify my stock cats, I am in the market for either another OEM set or an aftermarket 200 cell system since I still have to pass emissions on an annual basis.

Most of the current high flow cat offerings use an 'X' pipe after the cat and before the mufflers to mix the flow. My car will be street use 80-90% of the time so I'd rather not give up too much lower end torque.

I've searched extensively but the debate on whether the x-pipe configuration adds or deletes power has been hard to follow.

On one hand 'x' pipes lose power (post #67) in 2006:

https://rennlist.com/forums/996-gt2-...r-a-gt3-5.html

Followed by the introduction of an x-pipe system in 2011:

http://www.fabspeed.com/porsche-996-...rt-cat-x-pipe/





The dyno shot seems to indicate a loss of torque (20 ft-lbs) at 2700 rpm and continues to lag until the crossover point somewhere between 3500 and 5000 rpm.

Is this the case for all x-pipe systems?

I believe that the general consensus is that cat bypass pipes lose low end torque but give it back up high.
Any real world feedback or advice would be appreciated. I'd hate to go buy another OEM cat just to melt it again...

Thanks!

Cheburator

I have a 996.1 CS which was the first K400 car released by Manthey. I have a MM Exhaust with a crossover. The car does make 400bhp, so something must be working right... It is difficult to quantify though - I have MAF delete, equal length exhaust manifolds, 100 Cell cats and freer flowing mufflers, so maybe the 400bhp is the sum of all these mods.

It definitely made a big difference on my 928GTS 5-spd where we picked up 30bhp back to back with the help of a remap.

AudiOn19s

I did alot of research on this back about 4 years ago. Picked alot of brains of people with knowledge and real world dyno testing. I'm not an exhaust expert and won't pretend to be. I did as much research as possible on the exhaust on the market that actually made power on our cars AND on ones that sounded the way I liked and then I had a system custom built by a friend of mine to the specs I wanted. I know the before and after dyno results and I'm satisfied with what I've got.

**My personal opinion** is that the x-pipe is more about sound than anything else. My Belief (I'm choosing my words wisely here) is that if not executed correctly the "x-pipe" could actually hurt power in our cars. That said I have one on my car because that's what I was after from a sound perspective.

I'm not big on Modular exhaust setups because I personally feel the OEM diameter of the stock exhaust is part of what is costing power on the 996 GT3. I feel the fabspeed design posted is actually pretty solid for an x-pipe but I'd venture a guess the cats are the main reason for the power bump vs. the X design. I'd bet their standard sport cats without the x make about the same power gain over stock. It's all about the exhaust note you want.

Tonger

Thanks C'tor and Andy.

It seems like the main compromise in exhaust is between maintaining enough back pressure for the low end torque balanced against evacuating gas as quickly as possible at high rpm. In a way, this is almost like choosing between a camshaft that makes low end torque vs. one that makes great high end hp. I think that for my primarily street use, I should maximize the low end torque - or am I wrong?

Andy - did you use larger than 2.25 in pipes and can you share the names of the systems that made power on the dyno?

Thanks!

DRPM

I installed Cargraphic X pipe with 200 cell cats and cargraphic cans.
Very nice improvement and sound
Not as nice as my previous 4.0 but still gurgles well.