Theweezersdad

While researching various downpipes with a single set of cats, I've noticed some manufacturers (Renntech for example) have their cats located under the car (where the factory's second set would be), and others (Eurocharged for example) put them right behind the turbos (where the factory's first set would be). Am I looking at the right parts?
They all seem to have the oxygen sensor ports in the original locations. With the cats in the upper position (i.e. Eurocharged) the oxygen sensors would be before and after the cats. With the cats in the lower position (i.e. Renntech) the O2 sensors are before and after a random section of exhaust pipe.
It would seem the Renntech style would require a tune to cancel CEL's and maybe the Eurocharged wouldn't. Maybe they are in different positions for heat management?

https://www.renntechmercedes.com/ind...cat-gts-detail
https://www.eurocharged.com/ecutunin...less-downpipes

Any input would be appreciated.