It is a 500SE, it is a greymarket car, i removed the cat so i can have the car run cooler- which it has- and also for the power gain. I just want to know if i h ave to change the fuel mixture in order to make it run at optimimum level, since it has a more free flow exhuast system- im assuming its running to lean (?). I took it to my mechanics shop, but he had a stroke- and hes still in the hospital so i guess i have to just 'sorta tune it ' untill he gets better.