I just had the ECU flashed in my C63 and I'm very happy with the results.

I would like to add another cost effective modification that will increase the WHP without compromising the engine and overall reliability of the car. Any ideas?

 

Depending on what ECU flash you have..and how much your willing to spend..But headers/filters would be your next best bet. Followed by the heat spacers and thermostat kit.

For my C63 - I have Kleeman K2 kit and MHP Spacers/Thermostat with BMC airfilters....I thought about MHP Long Tube headers(more HP)...but didn't want to dish out more $$$

 

I have hears the headers are worth quite a bit of hp also.

 

Thanks! I don't want to spend the money on headers yet but how much WHP will I get from just changing the filters and what is the cost? I also heard that it would be a good move to get rid of the secondary cats.....do you agree?