944 exhaust questions

[Z06C5R]

Now that I'm through emissions for the last time, I'm preparing to pull the cat and run an after market exhaust. My search hasn't turned up anything in my price range, so I'm looking into doing a custom system. I was under the car the other day and I was very pleased with the design of the manifold thats in there, so I'm thinking of just cutting out the cat and running my own system from there back.

My question is, what is the approximate size of the stock exhaust tubing? Looks to be about 2 or 2.25" to me, is that correct?

Also, does anyone have any recommendations for mufflers? I run a Dynomax super-turbo on my Z and it sounds godly, but that's a much different engine. I'm a bit apprehensive on just slapping something on the Porsche w/o recommendations since it is a 4-cylinder and all...

[Techno Duck]

2.25'' and in some areas down to 2'' (such as before and after the cat). I highly recommend putting atleast a resonator inplace of the cat. The car is extremely loud with no cat and a straight through muffler (such as the Borla XR-1..which i also recommend highly).

Trust me when i say it is not acceptable as a daily driver with full 2.5'', test pipe and muffler. And mind you i am a young guy and like to hear my cars...and i also currently have my 951's wastegate dumping to atmosphere. Its to much for a daily driver.

[Z06C5R]

Yeah, I've got my Z to keep me (and the neighbors) more than satisfied with noise level. I was shooting for a lower volume with this one, so the thought of running a glass-pack in place of the cat did cross my mind... Should help to cut down on resonance too. I'll take some measurements this weekend and see what I come up with.

[flash968]

on a normally aspirated engine, if you don't want to lose torque, don't pull the cat - in a street car, the few hp gain (and it is very small) is generally outweighed by the low and mid range torque loss - on a race car this is not an issue though

[Z06C5R]

But it's such a hideous and evil contraption, LoL. Personally, I'm not sure how much tourqe there is to loose low end... IDK if it's just mine, but it sort of boggs up to about 3k, and doesn't really come on hard until over 4k anyhow. Sounds counter-productive by conventional logic, but maybe a small step-down through a 2" GP to supplement backpressure lost by removing the cat? I suppose I could keep it, but I imagine it makes the exhaust note all muddy like it is now.

[944 boy]

cut it out, just the cat wont make much if any difference if removed. If you go with a high flow muffler you might notice some loss in low end. I would personally put a resonator/second muffler in place of the car for better sound. It tends to get raspy without the cat. As for mufflers I dont have much experience personally. One of the best I heard was a borla muffler with a 911 megaphone.

[Techno Duck]

Stock cat in place with a 2.5'' catback sounded the best on my old '87 n/a. I eventually put on a 2.5'' test pipe...and kept it on about a week before i got absolutely sick of it. I noticed very little gains when putting on the test pipe..nothing worth dealing with the extra noise over.

Edit - Forgot i had these videos, some examples of what it sounds like. Mind you the video with the testpipe makes it sound alot better than it really was. Trust me, it sounded like crap.

http://www.youtube.com/watch?v=m0ABFz4793I

http://www.youtube.com/watch?v=Lmd4dFzIqrw

[flashgordon13]

I had the cat off of my car for a week and put it back. The engine lost a lot of low and mid range torque, but it did run slightly better a higher rpms without the cat. The sound was loud without the cat but I would have put up with it if the perforance was good, but like I said eliminating the cat hurt the drivablility too much to make it worthwhile.

[flash968]

we've done a LOT of testing on exhaust systems for the 968 lately - cat removal is good for about 15 ft/lbs of torque loss, but can give 3-4 hp at 6.5k (not much of anything below that) - probably about 75% of those numbers on a 2.5 liter engine

it also changes the mixture on cars with O2 sensors, as it changes the temp of the exhaust gasses - those cars tend to run rich, faking you into thinking there is more power than there really is, because the richer mixture adds throttle response off idle - however, it generally causes power loss through the mids where most people drive

[914efi]

flash968,

Could you elaborate on the mixture change?

Reason for asking is that I have a euro car, no cat, and was planning on a US engine install by just adding an O2 sensor into the euro exhaust. It does have a muffler where the cat is on a US car.

Thanks

[Z06C5R]

All the cars I've heard with the XR1 sound pretty good, but the tone seems very harsh (which should be expected with a race-muffler like the XR1 I guess). Everything else is a bit less raspy but can tend to sound a bit ricey to me... Perhaps my expectations are just too high - It is a 4cyl, after-all

I might go with a Dynomax superturbo - I love what it did for my Z, and they have a 90 day satisfaction guarantee, just in case I don't like the sound. I searched but couldn't find any videos of a 944 / Dynomax combo, so perhaps it will be a new combo?

[shikzachaser]

I used a small generic cat from Pep-Boys ($49) w/ ceramic coated MSDS headers and a stock muffler and tip. It sounds great, just enough to set off an occasional car alarm in a parking garage. I don't know if it makes any performance difference but it looks good and sounds good. The headers are relativly easy to install.



This picture was when I first did the engine. I have since replaced the fuel rail and done a couple other things. These are cool cars, I like it a lot.




Steve

[HondaDustR]

Yeah, I'd say try a free flowing performance cat with 2.25" tubing. Seems like it would be a suitable compromise between wide open and stuffed up. Having a free flow cat with no resonator might be just enough to take the edge off the sound without compromising flow too much.

Something like
http://www.***********************/details/QQPorscheQQ944QQMagnaflowQQCatalytic_ConverterQQ19 861989QQM6691006.html

I know it says it's for a 944, but it's obviously just a universal part.