Ghost944

i want to rip out my cat and put in a test pipe (im in ohio, no more e-check).
the porsche website says that the 944s without a cat have 18 more hp than those with one.
so i ahve two questions 1. is this hp claim true? 2. who sells these test pipes? can i just get one from my local muffler shop?

Serge944

The claim is untrue. There is a slight gain in the upper RPM range, but nothing even close to 18hp on an n/a 944.

The most cost effective way is to cut the cat out and weld in some 2.5" tubing. This can be done by any muffler shop, assuming that it is indeed legal in your area.

Dr.Porsche

Does getting rid of the CAT cause any problems with the motor i.e. O2 sensor?

Techno Duck

Removing the cat will only cause issues with passing any state emissions tests aswell as possibly creating less low end power due to less back pressure.

An interesting note is that the John Milledge reccommends running his most mild grind cam with no cat for best performance.

M758

no cat vs your current cat is probabaly worth 8-10 hp.

This has proven to be the case on 944 spec cars both on the dyno and on track.

Not sure what it does to the power band below 3500 to 4000 rpm however.

BTW.. euro cars had more hp because they did not run a cat plus had a 10.6:1 compression ratio vs the us car's 9.5:1. Also the computers were optimized for those condintions vs what we run here in the us. All together I it could be the hp difference we see. also remember the 143 vs 162 euro numbers are SAE vs DIN measurements so that also accounts for 2-3 hp difference with DIN being higher.

arbeitm

Just curious...what porsche website?

Crunky

No, the o2 sensor is before the cat, if it were an OBD2 car with one after, I can see how it might effect the one after the cat.

Before you do this have your car dynoed with cat, and with the bypass, there is always debate on this and I have yet to se hard facts.
I can see how removing a plugged up cat would increase performance, but the cat uses honeycombed chambers; the flow area inside the cat should be the same as the inside of the exhaust pipe, right? I could be wrong, but I want to see some hard evidence still.

smlporsche

OK, here are the FACTS as they pertain to my '89 S2

Bone stock after having the head rebuilt due to previous owners neglect - 186.92 HP - 185.90 ft/lb at the rear wheels.

After deleting the cat and going with a 3" Lindsey racing echaust with Magnaflow exhaust - 195.45 HP - 189.21 ft/lb.

The car is a dedicated track car and I did it as much for the slight increase in HP as I did it for the weight reduction.

Questions / comments??

Ghost944

but id like to know what i should expect just putting a test pipe in on my stock exhaust. also mines a 86 944

http://www.porsche.com/usa/accessori...s-porschecars/
then just select 944 and 1986 and click technical specifications
o and sorry its 13hp not 18 my bad

Diego

I installed a Bursch testpipe on my 86 na a few years ago. Mine has a resonator chamber where the cat. conv. would normaly be and the O2 sensor does mount onto the testpipe. I just did the testpipe and kept the stock muffler. It does have a nicer raspier growl now. Although I have not dynoed it I would say that I lost a little torque in the bottom end BUT gained a little more HP in the upper 4K to 6k RPM range. It might have just shifted the power band a little and maybe I didn't gain or lose anything, I don't know but it does feel a little different. I also have the K&N filter and Autothority chip and can't say I noticed much difference with either the filter OR the chip. A guy that I talked to from Germany who races Porsches there claimed that about the only worthwhile gain they noticed with the 944 na's is from running with no cat. conv. "testpipe". He also said they noticed little to no increase from a chip either other than the chip raising the rev limiter from 6500 to 7000 RPM so take it for what it's worth. It sure does sound nice with the testpipe though.

Robby

Remember than NA engines NEED a little backpressure, whereas turbo's do not- even still, I've seen several turbo's get test pipes & all they really gained was extra noise- very annoying- but, couple the test pipe w/a more open exahust, & you may find a few HP- one local 951S I'm aware of gained ~10HP from both- I don't think it's worth doing unless your exhaust is worn out, personally- in that case, especially in the case of a clogged cat (as has already been mentioned) & you might get more.

One thing to remember- if your's is a street car, you might want to weld a resonator in the center of the test pipe (again, has been mentioned) & I'd recommend a full 22"+ as opposed to a shorter one & then an extra muffler in the diagonal section, to help bring the noise back down- it's possible to have a larger, freer flowing exhaust that is actually quieter than stock, but it takes a little planning- btw, it's not very expensive either. The Bursch 2.5" test can ususally be found for just over $200 & you can buy any # of resonators &/or reso style mufflers (from places like Summit Racing) in either mild steel or SS (IF you want to ante-up for a full SS test pipe) to weld into places, etc, for anywhere from $50 - $150/ea. Local muffler shops can do the welding on-the-car for under $40/ea & probably cheaper if you take the pieces in seperately to do off-the-car. I recently had a Borla XR1 welded into the diagonal section of my SFR 3" catback for $30. If I knew before what I know now, I'd have had a 3" all the way back that was much cheaper AND a good bit quieter than what I have now. If it's a track car, noise doesn't enter into it as much, but I can tell you, from experience, that these test pipes, etc, will make neighbors (AND COPS) notice you- put you into the F&F ricer crowd real fast...

944Fest (aka Dan P)

Nobody has mentioned the cool "Flamethrower" option this pipe adds to the Turbos.

Wooombah! Wooombah!!

Robby

Oh yeah... OR the popping/backfiring when lifting off the throttle in neautral...