My research on exhaust and downpipes benefits to the money spent...

[Audi-RS6]

Lets ask; is it worth spending $5K on exhaust with downpipe and what is the benefit/gain are we getting?

here is the sample that RS4 has (best comparison picture I was able to find, rs6 has similar structure)

http://www.marksports.net/images/model/model_29_1.pjpeg

So ORIGINALLY we have 2 restriction points: 1st Cat and 2nd Cat

With Milltek they remove 1st cat and use HIGH FLOW 2nd cat
(you can buy one here:
http://www.merlinmotorsport.co.uk/p14033/JETEX-SPORTS-CATALYTIC-CONVERTER-130mm-DIAMETER-100cpsi/product_info.html)

http://www.merlinmotorsport.co.uk/images//exhaustsl/jetexcat.jpg

The end contain 2 silencers w/sound enhancement in both systems STOCK and MILLTEK


Now what is better: Cat at the beginning of turbo or in the middle?
I heard smth about back pressure, so if you have high flow cat in the middle it should create same back pressure as if you have only cat at the start point. Which means if you cut pre-cat your stock system in theory should perform same way as the $5K Milltek one.

Is it worth spending? I'm very sceptical about it now.
Espessially when I saw 11sec RS6 that 10secS4 has, with stock exhaust...

3" pipe is not a good reason to switch since if you indeed want it, you can ask muffler shop to change your pipes

[vangelis]

I believe it worth spending in good exhaust, but I believe the Milltek will cost around $3.5K USD not $5k. The was a qoutation i got for a 100CSPI down pipes with a non-resonated cat-back (without center silenser). you should gain around 20-30 BHP with this setup and even more with 3" cat-less down pipes if you able to find.

[10SecS4]

The only significant restriction in the entire exhaust system are the two pre-cats or "1st" cats as you'd put it. Gutting these two cats out yielded 1 tenth and 1 MPH in the 1/4 mile according to my back to back logs. This is on an RS6 that has already been tuned.

Recently I also gutted out the two main cats or "2nd" cats as you'd refer to them in your thread. I did not see any appreciable gains whatsoever, just as I had thought.

Looking at the OEM catback exhaust, I really don't think an aftermarket catback will result in any power increase, at least not at the power levels we're seeing with the stock snails. The factory catback is a really, really nice piece.

It's my opinion that the price of the Milltek catback/downpipes is not justified from a cost/HP standpoint. I say just gut the two pre-cats out yourself for $0 and call it a day. :thumb:
__________________
Marc aka 10SecS4

http://titsup-racing.com/video/rs6/rs6_sig.jpg

2003 Audi RS6
11.59 @ 118.63 | Video (http://www.titsup-racing.com/video/rs6/rs6_11_8.wmv) | Timeslip (http://titsup-racing.com/video/rs6/rs6_11_59_timeslip_resized.jpg)
Mods: No pre-cats & my own custom tuned ECU/TCU. That's it!

2000 Audi S4
10.73 @ 132.76 | Video (http://titsup-racing.com/video/s4/s4_10_73.wmv) | Timeslip (http://titsup-racing.com/images/s4/s4_10_73.jpg)
Mods: K04s + bolt-ons + weight reduction (bone stock motor!)


Lets ask; is it worth spending $5K on exhaust with downpipe and what is the benefit/gain are we getting?

here is the sample that RS4 has (best comparison picture I was able to find, rs6 has similar structure)

http://www.marksports.net/images/model/model_29_1.pjpeg

So ORIGINALLY we have 2 restriction points: 1st Cat and 2nd Cat

With Milltek they remove 1st cat and use HIGH FLOW 2nd cat
(you can buy one here:
http://www.merlinmotorsport.co.uk/p14033/JETEX-SPORTS-CATALYTIC-CONVERTER-130mm-DIAMETER-100cpsi/product_info.html)

http://www.merlinmotorsport.co.uk/images//exhaustsl/jetexcat.jpg

The end contain 2 silencers w/sound enhancement in both systems STOCK and MILLTEK


Now what is better: Cat at the beginning of turbo or in the middle?
I heard smth about back pressure, so if you have high flow cat in the middle it should create same back pressure as if you have only cat at the start point. Which means if you cut pre-cat your stock system in theory should perform same way as the $5K Milltek one.

Is it worth spending? I'm very sceptical about it now.
Espessially when I saw 11sec RS6 that 10secS4 has, with stock exhaust...

3" pipe is not a good reason to switch since if you indeed want it, you can ask muffler shop to change your pipes

[V8weight]

The only significant restriction in the entire exhaust system are the two pre-cats or "1st" cats as you'd put it. Gutting these two cats out yielded 1 tenth and 1 MPH in the 1/4 mile according to my back to back logs. This is on an RS6 that has already been tuned.

Recently I also gutted out the two main cats or "2nd" cats as you'd refer to them in your thread. I did not see any appreciable gains whatsoever, just as I had thought.

Looking at the OEM catback exhaust, I really don't think an aftermarket catback will result in any power increase, at least not at the power levels we're seeing with the stock snails. The factory catback is a really, really nice piece.

It's my opinion that the price of the Milltek catback/downpipes is not justified from a cost/HP standpoint. I say just gut the two pre-cats out yourself for $0 and call it a day. :thumb:
__________________
Marc aka 10SecS4

http://titsup-racing.com/video/rs6/rs6_sig.jpg

2003 Audi RS6
11.59 @ 118.63 | Video (http://www.titsup-racing.com/video/rs6/rs6_11_8.wmv) | Timeslip (http://titsup-racing.com/video/rs6/rs6_11_59_timeslip_resized.jpg)
Mods: No pre-cats & my own custom tuned ECU/TCU. That's it!

2000 Audi S4
10.73 @ 132.76 | Video (http://titsup-racing.com/video/s4/s4_10_73.wmv) | Timeslip (http://titsup-racing.com/images/s4/s4_10_73.jpg)
Mods: K04s + bolt-ons + weight reduction (bone stock motor!)
Question, did you relocate your rear o2 sensor bungs when you gutted your pre cats? Or did you just tune your ecu to ignore the rear sensors? I would like to gut my precats and relocate the o2 sensors behind the main cat, but I'm not sure there is enough slack in the rear os sensor harness.

[10SecS4]

Question, did you relocate your rear o2 sensor bungs when you gutted your pre cats? Or did you just tune your ecu to ignore the rear sensors? I would like to gut my precats and relocate the o2 sensors behind the main cat, but I'm not sure there is enough slack in the rear os sensor harness.

I took care of it in the tune. It comes standard in all my tunes. :incar:
__________________
Marc aka 10SecS4

http://titsup-racing.com/video/rs6/rs6_sig.jpg

2003 Audi RS6
11.59 @ 118.63 | Video (http://www.titsup-racing.com/video/rs6/rs6_11_8.wmv) | Timeslip (http://titsup-racing.com/video/rs6/rs6_11_59_timeslip_resized.jpg)
Mods: No pre-cats & my own custom tuned ECU/TCU. That's it!

2000 Audi S4
10.73 @ 132.76 | Video (http://titsup-racing.com/video/s4/s4_10_73.wmv) | Timeslip (http://titsup-racing.com/images/s4/s4_10_73.jpg)
Mods: K04s + bolt-ons + weight reduction (bone stock motor!)

[Audi-RS6]

to V8weight: If you gut your pre-cats or 2nd cats as I pointed you don't need to move 2nd o2s, since they are located before 2nd cats, just cut and drive without EC

to 10secS4: when you gutted your 2nd pre-cats and havent seen difference, then I think there is no point at all to touch exhaust


Question, did you relocate your rear o2 sensor bungs when you gutted your pre cats? Or did you just tune your ecu to ignore the rear sensors? I would like to gut my precats and relocate the o2 sensors behind the main cat, but I'm not sure there is enough slack in the rear os sensor harness.

[Audi-RS6]

did you take off downpipes without getting engine down?
any special procedures?


The only significant restriction in the entire exhaust system are the two pre-cats or "1st" cats as you'd put it. Gutting these two cats out yielded 1 tenth and 1 MPH in the 1/4 mile according to my back to back logs. This is on an RS6 that has already been tuned.

Recently I also gutted out the two main cats or "2nd" cats as you'd refer to them in your thread. I did not see any appreciable gains whatsoever, just as I had thought.

Looking at the OEM catback exhaust, I really don't think an aftermarket catback will result in any power increase, at least not at the power levels we're seeing with the stock snails. The factory catback is a really, really nice piece.

It's my opinion that the price of the Milltek catback/downpipes is not justified from a cost/HP standpoint. I say just gut the two pre-cats out yourself for $0 and call it a day. :thumb:
__________________
Marc aka 10SecS4

http://titsup-racing.com/video/rs6/rs6_sig.jpg

2003 Audi RS6
11.59 @ 118.63 | Video (http://www.titsup-racing.com/video/rs6/rs6_11_8.wmv) | Timeslip (http://titsup-racing.com/video/rs6/rs6_11_59_timeslip_resized.jpg)
Mods: No pre-cats & my own custom tuned ECU/TCU. That's it!

2000 Audi S4
10.73 @ 132.76 | Video (http://titsup-racing.com/video/s4/s4_10_73.wmv) | Timeslip (http://titsup-racing.com/images/s4/s4_10_73.jpg)
Mods: K04s + bolt-ons + weight reduction (bone stock motor!)

[mi021le]

well i love the car with the exhaust. sound and the boost hits alot harder. so to each his own. but only worth it with a tailored tune if u do. not just a stage 1 map.

[DHall1]

My .02c

Leave the exhaust alone for hp up to 550 and gut the pre cats for less backpressure. We have backpressure but the bigger problem is the size of our snails. Yes, we have small snails. I said it! Corky Bell says it too so don't shoot the messinger. Go read his book.

If you want more noise cut off the mufflers or buy xyz exhaust.

I like to use the old saying. We didn't buy Kia Rio's. These are 450hp supercars. There is nothing wrong with the exhaust. Just take out the first pair of green air cleaners. ;-)

I am happy to leave my RS exhaust alone. Its a work of art. Ditto for our E55. That exhaust system is full stainless and even bigger than the RS6. Both of them can handle all the flow needed for 500hp output. No problem.

Now, if we were looking to double or even triple our HP output then a full custom would be on tap. 20-30-50hp increases. Na. When I take a 220hp Supra to 500hp.....full custom is needed. When I take a 200hp Celica to 350......full custom is needed. I think 10secS4 drives this home pretty hard with his display of power on the stock exhaust.