SleeperX

What about replacing the primary cats with a high flow/racing cat? How much if any hp might be gained? Looking at Kleemann headers (which remove the primary cats) vs. other headers that leave them in place, I am estimating 10-15hp. ??

alroumi

I would suggest doing a Custom X pipe with Kleemann Sport cats, or SuperSprint X pipe with Kleemann cats; thats what I am doing for my SLK55.

ProjectC55

Just put on the Kleeman headers and don't worry about the primary cats bro! That's it. Did you see Chiromikey's setup? Take a look at it. Perfect example for your setup. Just keep your stck mufflers and put on high flow secondar cats. N/A PTE with his CLK55 ran 12.3 @ 114mph in the 1/4 mile minus primary cats ,kleeman headers,secondary 100cell cats,kleeman cam,full custom exh.