Hi all:

I just got my 997.1 C2S cab back from my indie mechanic. Among many other little things, he installed the 200 cell cats I picked up a couple of months ago from a fellow rennlister. Now I see what people mean when they say they really "wake the car up." The sound, the response, the subtle increase in power... all of it is great. I was thinking about adding PSE or other sport mufflers but I don't need to now; the sound is perfect even with the stock mufflers. And being a cab makes everything better! No CEL, no problems at all. I do not feel any lack of low end torque, though I would agree that the modest gains to be had are north of 5500 rpm. No problem! I usually drive around 4000 rpm anyway, lol, so with a quick stab of the pedal I'm there. I'm all set for summer!

Edited to add: these are the crossover pipes, not an x-pipe

 

You make me want these. Anyone use them in California? Any issues?

 

Most crossover pipes look stock when viewed from underneath. Not sure how CA deals with emissions but at least here in MA, they don't care how they look as long as there's no CEL and the sensors are "ready." I replaced my o2 sensors too and have had no issues so far.

 

What's the brand of your crossover pipes ?

 

You know, I'm not sure. I am the third owner of these pipes and fortunately for me they were obviously barely used. The only markings I recall seeing on them were "HJS" on each cat and, iirc, "Made in Germany." HJS seems to be the "premium" manufacturer out there, and most higher-end manufacturers seem to use theirs. Mine look suspiciously like AWE cats, but then again, just about all crossover pipes look the same to me .

Oh, the other thing they seem to do is to help with the power plateau I was experiencing around 2200-2600 rpm. It's not gone now, but it's less pronounced.

And some complain about the smell from sport cats - are you kidding me? Maybe I am as crazy as my wife and friends insist, but I LOVE the enhanced exhaust/fuel smell.

 

HJS are the good cats

RE CA, I believe they do not allow ANY modification and are trained well to spot them. When my brother in LA tried to buy my awe cats for me (to save some $$), the shop wouldn't even sell to him cause he lived in CA

 

previous owner installed high flow cats on his AWE system, still on the car. Has passed in CA twice before and now once again when I bought the car. The car was smogged by a Porsche dealership. Most techs won't care but some will.

 

Cats will move the torque curve down and get you smiling. Next: plenum/tb and chip.

 

I'm still not convinced that a plenum will do anything, but I'm going to try a flash. Just ordered Softronic yesterday .

 

IDP uses small dimples inside the plenum to aid in the flow of the air. Sort of like on a golf ball. But let's not get into boundary layer equations in here. They also do a better job at the Y junction to direct and flow the air than the factory plastic one.

 

The cats are the biggest restriction point on these cars by far, Sport Cat or Catbypass X-pipe really turns up the smiles per gallon factor. Glad to you are enjoying those crossovers! We made them for a bit before switching to the X, might be ours who knows haha.

 

I would love to hear this setup in person or on video....

 

 

I did not understand if on a stock car if it is better to replace the original cat with cat 200 cells , cat bypass , cat 200 cells ad x or cat bypass ad x .

 

This is all subjective, as I didn't have a chance to capture any good before metrics (dyno, 0-60, 60-120, etc), but I replaced the head pipes and cats on my otherwise-stock 9971. C4S cab with Soul's headers and 200 cell cats. Mufflers are still stock. The car seems to pull stronger from the mid-range up, especially when the variocam shifts, and there's a huge change in sound at mid-high RPM's on strong throttle. I have near-stock sound at low RPM/low throttle though, which keeps the neighbors and my family happy when they're in the car. No check fault codes either, in a few hundred miles of driving.

Which is better is going to heavily depend on your application.