CAT delete

[mayPOR944]

i have borla exust and new piping to the cat. I am wondering if i removed cat and just replaced it with new exust pipe, how would that sound and would it gain HP.

do the sell exust that bolts from the headers to the back before the torsion bar is
(the 3 bolts)

[porsche4life]

Theres my car with the cat delete and the factory muffler.... Not very much of a HP gain really...

[VII]

The sound can vary for each system so you'll have to try it and see how you like it. You will likely have a greater chance of rasp without one than with one. You can pick up high flow cats on ebay for cheap and if you go that route you would still pass smog.

[porsche4life]

See.... Thats the nice thing about OK... I have no worries about having to pass emissions....

[Rjackel944]

I'm running no cat and it sounds pretty decent. Its pretty quiet at idle, but pushing it past 3500 it screams. Sounds a bit raspy, and its quite loud, but i like it.

[Rudeboy42]

That looks like a wierd place to have an AutoX. What is it? Is it a small air strip or something?

[M758]

I belive replacing used stock cat with a test pipe is easy 7-10 hp peak. It may not help the lower end of the curve, but the upper end it helps. The muffler is not big factor. I run stock headers, test pipe and stock muffler. The car is not very loud and make good power. More than if I had cat in there. Plust a cat is 10-15lbs of extra weight.

[dryslick13]

You might want to look at a Bursch exhaust. They sell headers that come with a cat delete pipe. I bought one for $315 and it bolts right up to the stock muffler. Also has the bung for O2 sensor so it is a direct fit. Makes a very racey sound combined with my magnaflow muffler. Car feels like it has more power in the mid to upper range.

[HondaDustR]

Yeah, it depends alot on the system you are running. I messed around with this and certainly found a couple things that don't work well together, depending on your goals, mostly regarding rice tolerance and noise tolerance. The stock muffler won't sound much different except a little raspier in the midrange with a test pipe or smooth tubed glasspack resonator like the Thrush parts. A gutted stock cat is a compromise. It doesn't sound anywhere near as raspy as a test pipe or a Thrush glasspack resonator, but it will not flow as well due to the big empty chamber inside that can act as an expansion chamber and affect exhaust scavenging. The little cutouts protruding into the stream as seen on the tubes inside "turbo" style mufflers and most Cherry Bomb glasspacks apparently help cut down on the high frequency noise, but I opted for the Thrush because I didn't know that at the time and their abscence looked like it would flow smoother. It was not far off from a test pipe, and these motors are very loud and raspy without the right sound control.

Increasing the exhaust flow may or may not change much depending on your tuning. I can't speak for the stock tuning, but many people say they lose low and midrange by going to a test pipe/gutted cat. The way the Motronic works, especially at WOT makes it a relatively rigid system that doesn't compensate well (or not at all in the case of WOT) for changes like that. I've since been running Russel Berry's 944MAX chip that I am told was tuned to work optimally with a test pipe. I should say that it felt noticably stronger, especially up top with the Thrush glasspack in place of the cat and a Thrush welded muffler (basicly a Flowmaster 40 knockoff) versus stock. There was no noticable loss in the low end, but the butt dyno is not the most accurate thing in the world.

My experience has been as follows:
1. Gutted cat with stock muffler: A little bit of raspy howl around 3000. No other noticable increase in sound level or quality. It did seem to help the top end out a little but hard to say.
2. Gutted cat with 2 1/4" Thrush welded: The raspy howl around 3K turned into a much more objectionably harsh rasp, but not too bad. Sound quality was pretty good in the mid/top end, but a little too loud for daily driving, and way too much low frequency resonance at 2500 and below. Throttle response quickened up a bit and it felt a bit stronger up top, too.
3. 25" long 2 1/4" Thrush glasspack in place of cat with Thrush welded: It would be ok on the track, but sounded positively aweful. Even louder and very harsh and raspy. It did run nicely, though, with peppy throttle response and good pull through the rpm range.
4. 25" long 2 1/4" Thrush glasspack in place of cat with stock muffler: Sounded like a much quieter version of the horrible raspy nastiness, but was really only nasty sounding around the 3K mark. The throttle responce seemed to take a slight hit, but the extra butt hauling sensation in the mid/top end was mostly retained.
5. Stock cat with 2 1/4" Thrush welded (current setup): Very nice smooth throaty sound that has practically zero rasp and is not too loud but definitely louder than stock. Throttle response is still a bit quicker than stock, but the mid/top end just doesn't feel as free with the cat as it did with a smooth resonator. It still runs well. I decided a couple hp was a fair compromise for pretty much nailing down the sound I was after.

Someone posted good sound results with a high flow magnaflow cat and what looked like a Dynomax bullet resonator combined in place of the factory cat.

This was also recommended as a very good cat delete replacement that cuts down on the rasp.
Corvette Exhaust System, Sidepipes, Mufflers - Sweet-Thunder.com - Chambered General - Main page

Someone else recalled a recent Excellence article recommending running a dual tip muffler and using resonator tips to get a smoother sound.

Here's the details of my experiment. http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/543375-what-aftermarket-muffler-type-muffler-makes-these-cars-sound-good-2.html
And a video. I still need to record what the current system sounds like, as it's by far the best of the different versions. YouTube - Porsche 924S Thrush exhaust project

If I had money, I would try the Bursch 4-2-1 header with test pipe and a Flowmaster 60 muffler.