I installed my cat-less down pipe. I really can't believe the difference it made. It has more torque and sounds great. With the RMW tune it has always been able to brake the front wheels free when you rolled the power on in second gear, but now I have to be very careful, it doesn't take much to brake them free. It has a JCW exhaust and Mark had the resonator removed. Now the sound it makes is Great! To keep the check light from coming on I got 2 spark plug extenders and put them between the down pipe and the post cat O2 sensor. The one the O2 sensor screws into has to be drilled out so the sensor can fit into it. Next time I have the car on jack stands I will do a how to. I have driven the car several times with no code.