stephens

I have seen numerous posts on MBWorld and other forums statiing that MB's lose performance if cats are removed. This is completely contrary to what i understand about engine tuning. Now I'm no engineering genius, but I always understood that backpressure on an exhaust is bad, no exceptions. I understand that the fuel/ignition map needs to be changed to compensate for the changes, but not that the backpresure actually helps?? Am I missing something?

pocholin

I've been talking to a guy in Dubai who sais he removed all 4 cats (pre-cats and cats), he says there is a nice difference in improvement, I am tempted to do the same and make it a bolt on so I can put it back on to pass inspections here in Houston.

He also says it sounds great and not too loud, I'm more worried about making it too loud.

jswedberg

Backpressure is NOT bad. On most engines, backpressure will increase torque in the lower rpms. It is very difficult to improve the stock exhaust systems on Mercedes or Porsches (or other fine cars). Most companies that claim more that an few horsepower (5% or so) are blowing smoke, and many actually lose horsepower at other than max rpms.

There is a short article in the most recent Road & Track magazine about this, but they don't go into detail. They do say, though, that backpressure increases engine efficiency at certain rpms.

There will be a audible difference, however. And, at least in many parts of the United States, you will not be able to pass emissions inspection.

My opinion, of course - having been through the whole Porsche exhaust deal a couple of times.