Please excuse my ignorance, but the only time I've run straight pipes was on a carburated motorcycle and it ran like crap due to loss in back pressure that was required for low-end torque. Does the stock ECU on the allroad adjust fueling to account for loss in back pressure? My objective is simply this:

1. Prolong the life of turbos (gut the pre-cats.. understood.. ok)
2. Run as much straight pipe as possible without being obnoxiously loud.
3. 1 + 2 and avoid CEL (de-foulers work on straight pipes? If not, how avoid CEL?)
4. 1 + 2 + 3 and make it CHEAP.

I was thinking of having a muffler shop simply cut-out the crap from the exhaust system and replace with straight pipes all the way through. Besides the loudness factor and better turbo cooling, is there any downside to this setup? Is running full straights bad for the engine? Should I keep the cats and run a straight cat-back?

Stock ECU only here. I have a TIP and absolutely don't want to chip the car for power.

Opinions?

 

If you are concerned about CELs, I would not remove the rear cats. Here's my sad experience. Due to failing cats, I replaced the system with a Billy Boat downpipe kit that eliminated the front cats. I replaced all the O2 sensors with oem Bosch. It kept throwing codes. I installed antifoulers which did not help. Still get periodic cat CELs and now I have a failing SAIU according to a third CEL. The car runs fine (other than the CEL being on most of the time, until I clear it) and the mpg remains unchanged. I will probably have to replace the SAIU this fall ($700) since it makes a godawful noise on start up when the weather is colder. FWIW, the car also has 206k miles on it.

 

SAIU is the secondary air pump right? I believe that can be deleted along with some PCV hoses. If it fails on me, that's exactly what I'm doing... get rid of it altogether.

Back no topic, did you run a true straight pipe or left the back cats still on?

 

For a around 200-300 you can get the rear O2 coded out of the ecu. That will make the car automatically pass readiness and never throw a code for cats effiency.

 

New aftermarkets cats tend to fail readiness codes and trigger a MIL.

So with that said..... Just imagine what your going to go thru with what you want to do.

The thing is.... removing cats is supposed to be better to force induction, thats why they make downpipes. But you need to be able to adjust fuel mixture, Audi does it within a certain parameter, if it can't adjust enough to bring it where it needs to be (emissions) it will throw a light.

As with anything performance. You can't really just change one thing. It either doesn't function to its potential or end ups hurting the car.

 

AudiTek's answer about aftermarket cats sums up my situation although ECS Tuning said there would be no compatibility problem. The Billy Boats eliminated the front cats and provided aftermarket rears. The CEL goes on anywhere from 20 to 200 miles of driving. The SAIU just started acting up a couple months ago. Right now I am not driving the A6 much because I drive a Crossfire roadster in the summer. I did NOT install the test pipes - they are sitting on a shelf in my garage.

I'd like to hear more about how the SAIU can be removed. I thought it was required for emissions (not an issue here in MI) but I don't want the A6 running worse. If I have to throw $700 at it, it will be the second major repair this year. Not a terrible thing on a 9 year old car with 206k.

I have an GIAC chip. Do you think they can re-code it to remove the rear O2 sensors?

 

That's what I'm saying. Does the stock ECU adjust fueling to account for straight pipes? Somehow I don't believe so, but I want to hear experiences. Are you suggesting that straight-pipes will make the engine run lean on stock coding? If I keep the rear cats and delete everything else would that be any better than full straight?