I have a 2003 Coupe. The follows mods are intake, plenum spacer, and tune. I was thinking about getting HFC installed. This is the last modification that I was going to do to the car. Would spending $650.00 be worth it from gains that I would get from the HFC? Any help would be appreciated... G U LATER!!!!

 

In my opinion, no, they are not worth the cost. Now if you need to replace them anyway (worn out), sure. The cost/hp benefit is just not there unless you are going FI.