although i've only been in the audi world for about 6 months, i have yet to see a car with absolutley no cats. Probably for a reason, but besides passing emissions is there another reason no one removes all the cats? Obviously the check engine light would be on, but as long as its not going into limp mode or affecting performance in any other way i assume its ok?

 

as long as you leave the O2 sensors in the down pipe it wont throw the CEL on the computer cant see the cat only the O2 sensors ans that's why people are fitting test pipes which is the same thing as removing the cat

 

has anyone lef the precats in place, but just cut out the factory second cats and replaced them with a test pipe? thats what id like to do

 

i could be wrong, but i think the CEL will still go on regardless if your o2 sensors are in or not. the reason being is for emissions. from what i know, the o2 sensors look at the air/fuel mixture before and after the cat. and without the cat, there will be an abundance of hydrocarbons leaving the exhaust. but if you do want to go catless which i plan on doing fairly soon, you can go two ways to pass emissions and get rid of the CEL light. one, and more expensive is chip tuning. i know unitronic will do this for you. www.unitronic.ca. the second option, which is cheaper and probably the route i'm going to take, are getting o2 sims. that's my input. let me know if i said anything that's wrong

 

that sounds good, and if i go catless ill get the simulators as well, unless stage 3 awe tuning turns them off for me.. can anyone confirm that?

how beneficial will it be to remove secondary cats yet leave the primary ones? (only asking because i dont want to remove my dp's to hollow out the preliminaries) so i was just gonna leave em and cut out the secondaries and weld in a test pipe

 

First off there are 2 cats per bank So 4 cats total. 2 are right off the turbo, & really hurt performance. Most people will gut these out on stock downpipes.

The secondary cats are no where near as bad. Really you loose a couple of HP there.

There are a few companies out there that make downpipes with out cats in them, there also cheaper with out the cats. ASP, AWE, etc....

You can get a "STG II chip" that will shut off the secondary O2's so you don't get the CEL.

 

i know there are 2 cats/bank, i didnt know the prelimary one was more restrictive tho. i guess i assumed that since the secondary is larger would be more restrictive

 

I don't have cats in my car and it runs fine. Not having the cats in will effect the long term fuel trims but not enough to do harm to the car. I do not have a CEL for the 02's you can get around that by going to your local auto store and getting spark-plug non foulers part # 420002 put one in each bank and you should be good to go it worked for me.

As for Dp's I would suggest getting either stock modified Dp's (vast performance) or modify your Dp's there are several S4 owners out here with the piggie pipes and for the money you can't beat the performance. Just my 2cents but I own a 4.2l so what do I know

 

show me pictures of 4 catalytic converters on one V6 car or dont you mean ( 4xO2 sensors )

 

Here you go Dave,
http://www.audiworld.com/tech/eng75.shtml

I would suspect your guys don't have the pre cats, since your HP is 258 & we get 250hp over here. They really kill turbo spool up.