Downpipes.. good or bad idea?
 

Alright, been mulling over bringing this up, but what the hell its monday...

So I am using a VW/Audi performance shop to do the work on the 01 2.7t MT A6 I got recently. When I brought the original heads in for evaluation a couple weeks ago, we got to talking about modifications. I brought up piggie pipes and beyond the inspection/emissions issues that might bring up in various states, it was the shops stance that removing the pre-cat modifies the conditions and parameters the ECU is controlling the engine at which are all things that were engineered by the designers for a specific range. Moving things around or changing things like gutting the pre-cats changes those ranges. Furthermore, it would put additional load on the main cat and cause premature failure.

So is this a valid line of thinking? I have read many threads on piggies and exhaust mods and I haven't ever seen this point brought up and I also have not seen a bunch of threads about failed cats. So why would a performance shop be against this mod? Could it just be that advocating this mod is encouraging people to break some states emissions regulations/laws? Or is there some actual truth to the modification theory having adverse effects? (granted modifications always have that potential, I am speaking about in this instance since so many people have done it)

It seems to me that besides the better flow from less restriction, another benifit of the pre-cat removal is less heat generated under the hood and less wear and tear overall on the engine by that very change.

Thoughts?

its true that those values change but that is why you relocate the 02 sensors behind the main cat. Youre thinking is correct but the pre cats are there for emissions reasons. It lessens the carbon footprint and reduces taxes in some countries. Otherwise they serve no real purpose and should be removed. Piggies all the way as long as they are done properly