Hey guys,

I am thinking about improving little performance and exhaust sound by removing secondary Cat.

however, I don't know much about good idea of this.

I had b5 S4 w/ Stg 3 and did not had any issue with o2 reading or fault code.
how is with W209 55?

Can I just remove it with straight pipe? or any better lower sup?

please give me suggestion with experience

thank you

i have a w208, but i just had the secondary cats and resonators removed. no CELs or issues, just put in a straight pipe. I believe the w209's only have the cats and no resonators and people have just replaced it with straight pipes with no issue. just so you know, you'll feel a little loss of torque in the lower end.

Sounds pretty simple,

so If I lose bit low end torque, what's my gain?

i would say when you punch it at highway speeds, it builds up faster. also, sounds sick.

No resonator in the 2003 CLK55.

in my W208, i removed the secondary cats, resonator, AND muffler, w/o any CEL's coming on. Because I lost low end, I got my car's ECU tuned by Speed Innovation. That solved the problem and made the car so much more responsive!

Has anyone who has completed the above discussed modifications dynoed their car to see if there are actually any improvements? This would be good information for the forum because it is a potential modification that only requires removing parts and not spending on new parts in order to obtain better performance results.

i'm gonna do this soon i think. it's been bugging me for a while. i'd like to take advantage of some reasonable priced headers too! i'm wondering what to do about ECU tuning to match higher flow filters and exhaust...