What are some fast ways to modify a 2002 C240 to give it some more horsepower and how much diff will it make?]

 

I used a K and N air filter. it doesnt do anything dramatic but it is said to add about 5+bhp.

 

For a basic mod, there are evosport pulley kit and ECU programming avaialble. Also K&N filter as C280 SPORT mentioned.

 

Actually i think recently B&B came out with an actual intake system. It comes with both intakes and is better than just putting in the filters. Also exhaust will add some HP too. look at Remus or weltmeister. i will post the site of the B&B intake if you'd like