high flow cat?...
 

I was trying to decide if i wanted to install a high flow cat, I was wanting to quiet the car down some. what differences would I notice if i did install one? would i be able to notice a loss in performance? would it be any quieter? how much?....

Well for performance you will not lose power, you will gain alittle. (thats why its high flow). sound wise im not so sure should be the same, or more quiet.

If you've removed all of your emissions equipment, you might as well go with a Racing Beat presilencer. I currently have a 2.5" high flow cat and it flows just as well, but believe it or not it's LOUDER (probably because it weighs 11 lbs. vs. the RB presilencer, 16 lbs.). Just make sure that you buy or fabricate a block off plate for the split air pipe opening. You might lose a little top end, but you'll most likely gain a bit more midrange power.

Wait your saying a hi flow cat will gain power over a straight piece of pipe?

What marketing BS are you buying into?

It will flow better than a stock catalytic converter.

Also, I've heard stock cats with no air pump, overheat and melt the material inside. Would a high-flow converter melt without an air pump and air pipe attached.

explain block off plate for the slit air opening...

http://www.2751engineering.com/2751parts.html

--Gary

whats the purpose of the block off plate?...

I've had my car 4 ways with otherwise the same exhaust:
1. OEM cat. Quietest of bunch.
2. 2-21/4" straight pipe. Loudest of the bunch.
3. Edelbrock 2.5" muffler, straight through 12" body. You wouldn't think it would do anything, but it was MUCH quieter than with the straight pipe and a bit louder than with the OEM cat.
4. 3" Magnaflow cat. Personally I expected this to be the quietest next to stock. It turns out it was a bit louder than with the muffler.

Performance wise I can compare the muffler to the straight pipe. The pipe caused the boost to increase substantially at the low end. It made the car very torquey and while not relevent to n/as, it shows the back pressure decrease. With the muffler, I think the peak HP, was probably similar, but it clearly had more back pressure. I massively ported my wastegate when I changed to the magnaflow, so I can't comment on it's performance.

If you buy the racing beat presilencer, it comes with a tube that a pipe that extends from the air pump would normally connect to, but if you removed your air pump, then you wouldn't have anything to bolt up to that hole, so you'd have an exhaust leak. The block off plate is so that you don't have an exhaust leak.

Buy the racing beat 3" turbo presilencer that normally comes as part of their 3" turboback 87-91 system. IT'll make your car sound similar to my old vert. I have it on my FD, with an otherwise straight 3" system, and it toned it down a lot. IT is worth the money they charge ($250), but sometimes you can find them used.

will removing the Split air pipe on a s4 T2 cause any problems????

If you ditched the cat already you can ditch the SAP.

I know on the s4 N/A it opens the 5th and 6th ports, just wondering if on the s4 T2 if theres any use for it other then putting air into the CAT???