[AMS Performance]

Its not so much back pressure, as it is how the entire system is designed. If an entire system is designed to have constant back pressure throughout then you won't necessarily lose torque, even if back pressure is less. But if you have a restrictive bottle neck in the front half of the exhaust system, then all of a sudden put on a larger diameter pipe exhaust at the end it can cause a reduction in torque b/c of both back pressure loss but more importantly reduction gas velocity. If you are going to upgrade your exhaust you have to upgrade the entire system (especially the cats) as a whole, not piece by piece. Also, many people do not use mandrel bent piping, they use cehaper kink bent pipe, which also reduces performance, yet they blame "lack of back pressure" or something else when in reality that's not the reason, so its impossible to say why you feel you lost torque, the exhaust you are running may have not been built properly and is impossible to say with out any pictures. There are so many factors that can influence performance so you cannot just say reduction in back pressure = bad or some similar generalized statement.

clk55 W208 stock exhaust is an excellent candidate if it is a direct fit, its 100% free flowing resonator & muffler.

search on club202 for the thread for the C36 exhaust internal pics, I believe it was posted by "23K" if I'm not mistaken.