Paladin_1977

Guys,

I want to know if it make sense to install a X-pipe or other headers if I still keep the catalytic converter? For my understanding are the catalytic converter is the bottle neck in the exhaust system, right? So, any replacement with keeping the catalytic converter is non-sense - or do I miss anything?

I have already a flowmaster muffler but the remaining parts are stock.

FYI: I have to keep the catalytic converter to pass the state inspection in Germany.

Dan

SamsBlueGT

Contrary to popular belief, most of today's catalytic converters flow air quite well. I would keep cats in your equation. The only difference is really the sound. A cat-less exhaust system will sound more raspy. You're not going to gain any power by removing cats.

But you don't have to take MY word for it...

http://www.kennebell.net/techinfo/fo...Converters.pdf

Derf00

Not mention, virginia is very strict on their emissions laws, no cats, no pass. If you're worried about having cats on your car because of "restrictions" get some highflow cats. Those are usually legal in 50 states as long as they have a CARB#

Nuke

If you can legally do away with the cats, then you'll see some decent gains. LT's will provide nice gains with a good percentage of that being from losing the cats. Other than that, the stock exhaust flows very well. There's very little HP gain, if any, going from the stock H-pipe to an X unless you go with an O/R X.

Since you can't lose the cats, you can go with hi flow cats which will provide modest gains over the stock cats.

SamsBlueGT

I know from previous encounters with you that you usually know what you're talking about. Can you provide me with some proof that stock Cats VS no Cats VS high flow Cats have any difference in RWHP? Keep in mind, most times people will post before and after dyno results with more than just one item being changed, thus invalidating any claims that any ONE part caused the RWHP increase. That's a big reason I trust what Kenne Bell has to say on the subject (see the PDF I linked to further up this thread). Kenne Bell has done very extensive research, dyno proven, on what items impact RWHP and what items do diddly squat.

I'm not saying I don't believe you, I have just heard many conflicting things on this very subject.

Paladin_1977

@ SamsBlueGT: Thanks a lot for the link to the Kennebell homepage. I think their test results are not faked. For that reason I will keep my stock exhaust and tweak my shaker system to route pure cold air to my filter box. My current air flow is mixed (hot and cold).

Also, I will try different fuel grades with some updates of the Bama tuner.
In parallel I am going to change my brakes.

Thanks a lot guys.

Nuke

SamsblueGT:

I don't have links to provide to support the cat question on impact on RWHP. I'm sitting in a hotel room at the moment and not about to do an extensive search. But there are quite a few forum members here and on other forums that have deleted the OE cats or went with hi-flows, some of which have dynoed and others that haven't. Quite a few that have gone with LT's and no cats state their belief that about 1/2 of the gain is the deleted cats. It only seems logical that deleting the cats or going with HF's allow the exhaust to flow more freely. I wish I DID have something more substantial to provide you.

SamsBlueGT

@ Paladin: Glad I could help! They were really helpful to me when I was deciding on my supercharger, and talked with me on the phone for quite a while answering my MANY questions. Great customer service, and they really seem to know what they're talking about.

@ Nuke: In my generally technical mind it makes sense that deleting Cats or going with a high-flow version would increase airflow, which in turn SHOULD decrease resistance and therefore increase RWHP. I do notice that Kenne Bell's research seems to say the opposite though...which if true would suggest that there's enough flow in the stock cats to not impact performance in any way. Again, unless I see back-to-back tests with only changing one part at a time I am a lot less likely to believe that any one part is doing X % of the gains. That's just what I've learned through research. I know LTs in themselves do provide a bit of a gain.

Throck!

You can install a cut out system before the cats if you're really worried about it, open them only when you need full power, take to a dyno to find out if they make a difference or not.

As for headers, I installed headers and cams at the same time. Not sure which made the difference, but my power went up about 30hp and boost went down from 8psi-5psi. I'm sure the stock system will flow with minimal headloss until whatever KB says, but opening the system up did make a slight difference for me...the power gain and exhaust headloss is probably just proportional (%) to how much fuel/air you're pushing through the system.

Headers and cams made a huge difference in volume, turns out an x-pipe helps quiet it back down about the same way Bose noise cancellation headphones work. It's still louder than it was, but it's now bareable.

I started off with an off-road H-pipe, then reinstalled some hi-flow cats to try to quiet it down, they didn't help much at all. I didn't dyno before/after the cats, but I didn't notice much difference.

Hopefully this makes sense and is on topic, I'm tired.

7gtthrilla

Actually, it's fine to keep the cats on it, no harm in doing so and to be completely honest with you, taking the cats off are only good for sound. It actually takes a few hp away, but it's still a great mod to do.