Doing an exhaust system and trying to decide between a muffler with a cat vs. one with cat bypass. I know the catless version will be cheaper, make more power, and be louder. What kind of power difference will there be between the two setups if everything else is the same? A rough estimate is great.

 

i'd love to know the answer too.

 

A street muffler on a 911 Turbo will always sacrifice power given the little space that is available between the engine and the rear bumper.

To refresh the facts about the 996 TT exhausts here is some info :

The stock exhaust has 0.36 Bar backpressure at about 6800 rpm.

1. the 100 cell cats ( cell number , lenght and diameter of the cat determine the backpressure )

2. the 90° transition between the cat and the muffler ( radius and diameter of the bend determine the backpressure )

3. the muffler itself ( diameter and configuration of the inner tubes ... )

4. 180° turn of the airflow inside the muffler

5. 90° bend and diameter of the outcoming tubes

A well designed muffled exhaust will have a backpressure of about 0.089 bar. Subtract the backpressure from boost and you will have actual utilized boost. The number will vary depending on power being produced. On a stock 996tt it looks to be about 12 hp. As the power produced goes up the loss will be the same fraction of the whole.

 

HAHA Awesome!

 

that's one hell of an answer! +1

 

I agree....I run fabspeed loud gen 1 and have switched back and forth between that and catless straight pipes, and no mufflers and the 100 cell and could tell Zero difference other than the noise. Maybe 5 hp at best??? if anything it lost torque down low. I even put the stock gt2 exhaust back on and it killed it....bad..

 

cool. I was looking into getting the complete fabspeed setup with the 200 cell cats vs the cat bypass pipes. I didnt know fabspeed offered 100 cell cats, I only saw 200 cell on the site. How does the car sound with the cats and the muffler?

 

They do not offer 100 cell any more...the gen1 100 cell is kind of hard to find...as they work really well, kind of loud but I like the sound...you can find they in the for sale section every once in a while.

 

Chad, you never stop to amaze me with your answers!! I don't think anyone else on the forum would get into that much detail (and there is nothing wrong with that because we all are here to learn)!!

FWIW I have a Switzer Cat Back with 200cell cats. The exhaust is a 70mm, 2.75", design. When I have that on and my boost controller turned off the car makes 490rwhp on 14.xpsi. With the straight pipes on the car makes 15.xpsi and 530rwhp.

 

Powell,

I'd love to take all the credit, however the information was given to me awhile back by Steff from Europipe when we were deciding what to use for an exhaust on my new build.

 

you live in Florida, no emissions standards run the straight pipes

come to one of the track events and drive my car

 

Wow, that is a SIGNIFICANT power difference. Much more than I expected based on cjv's response.

Yep, I have run catless cars almost all my life, but I was thinking that it might be a bit much/ricey for a 996tt. I know your car is a 110% track prepped, so I wouldnt question straight pipes for you. Do you think it would be too loud, or attract the wrong type of attention on the street? I do like to let the car breathe in the high RPMs occassionally..

 

Keep in mind the information Chad posted is talking about going to an aftermarket muffler/cat setup. I'm going from 200 cell with a muffler (that is 2.75") to a 3" straight pipe from the turbo back. Plus I have a larger set of turbos than most, which is why the gain is so large going to a straight pipe.