silverbullet

I want to get rid of the cat really soon. I can't really afford a full 3'' SFR exhaust right now. So I was going to have the cat replaced with a 2.5'' pipe.

The question is how big a difference is between a 2.5'' cat-less and a 3'' one? Is it even substantial enough to notice? I just was thinking that getting rid of the clogged cat will give the most gains anyway.

Thoughts?

aeronautica86

as long as you have the stock turbo, I would suggest you just go to an exhaust shop and have them cut out the cat and weld a straight pipe in

TRWright

I picked up almost 25hp and 30 ft/lb tq when I had a straight pipe put in place of my cat. I also reached 15psi over 200 rpm sooner. (The car had about 80k miles at the time, original cat.) The only other mod was APE MAF, and I was running 15psi.

silverbullet

Cool, thanks guys!

My car has right around 83k miles on it and everyone says that the difference in removing the cat is dramatic.

2.5'' vs 3'' pipes really shouldn't have that much difference in power unless you're really modded, correct? Once the cats out, the rest is just picking up small gains here and there.

Ahmet

I just find this so hard to believe. I did not see even a 10hp difference on more than one 944 turbo (k26), but we shall see, we shall see... You guys will make me test this out for myself, again, but this time w th/a before and after and cat removal being the only modification. I will try to test on the same day if possible.
Ahmet

Trucho-951

I noticed a difference when I did mine on my 110K car, but I would not call it "dramatic".

tedesco

can support tedwrights experience. On my (chipped) turbo S it made a big difference. Boost coming in about 300rpm earlier and noteably more power and responsive. I also heared the turbo wistle again. Certainly it depends on the age of your cat and how the car was driven. My car was used as a track day car for about 3 years which might not help keeping the cat in good condition. After I removed the cat I inspected the ceramic converter cell just to get an idea in what condition it was. I was realy surpriesed to see that no cells were blocked, nothing was broken or "melted". After the inspection my expectations about power gains were very low and the bigger was the suprise when I drove the car the first time after the change.

evil 944t

I know of a couple cars making between 300 and 400rwhp with a 2.5" full exhaust. Defastest is making close to 500 rwhp. 3" isn't a must have with a stock turbo. I think it just helps quicken up spool time and brings on your torque curve to the left.

SD Porsche Fan

Seems like this topic keeps comming up.

https://rennlist.com/forums/showthre...ght=cat+delete

My cat was pretty clogged up. I was only achieving 7.5 psi and it wasn't comming on until abou 3500rpm. I had a shop weld in a pipe and was able to get 11.5 psi and spool up came on at about 3000 so I noticed a big difference.

I was able to get the cat cut off just before the brackets and preserve the basic geometry of the exhaust. This made the re-install fairly straight forward as I just bolted it up the way it came off and didn't have to fabricate any brackets or clamps.

Mike1982

When I got my 3" fabspeed SS put in, I saw that my cat was out when I looked at it. The first two cells where busted out and melted to the last cell, not so good of performance! So then after putting the next pipe on I went from about 14.5 PSI up to 17.5ish. Not to sure how much I picked up because I turned the boost down right now! It does spool up very nice now too. I don't think there is really any difference over a 2.5 and 3.0 for about 95% of the people here. I went to 3.0 because it was stainless and if I was going to put down some cash for a testpipe I would like to put something very nice on. The 2.5, as far as I know, are painted so they still can rust if you drive your car in the winter/over a long time.

PorscheDoc

I plan on putting on a 3" lindsey exhaust in place of my 2.5 (no cat + magnaflow muffler), i will do dyno before and after to see a difference, but i probably won't get around to it until after xmas. I would imagine going from a 2.5 (catless) to a 3 (catless) is probably worth 10-15hp, but that is strictly a guess.

HIGHBOOST

I plan on going to a Muffler shop and having them bend some 3 in pipng for me. It is actually less expensive that way. As for the posts above, with stock turbo and chips 2.5" is sufficeint. I jsut think that you should go with a 3" now, so you don't have to worry about it later on.