The header is without a doubt the best performance upgrade so far to the pro5. I have a injen cai and the exhaust is done to 21/4 to a ractive muffler. The car pulls nicely throughout the power band. I used to have problems with throttle response but now the car just goes and goes. I haven't dynoed the car but the header makes one hell of a difference. Overall if anyone is looking for a perfoemance upgrade and wants to stay n/a the headers are a must i am still waiting to her from perfurmworks( i think that is his handle) about a tb and intake manifold. The header gives me a little more hope in staying n/a. The design is very nice, the welds are nicely done by AWR, who must commend for a great product and interest in making parts for the pro5(which many companies ignore) and the install was not very hard (suggest doing after the car has been off for a couple of hours) I removed the radiator, i had a lot more room to work with. I have had no problems with check engine lights, and the header sounds great to me, the sound is fuller than before and can get a little loud but if you are worrying about making noise performance may not be the best way to go. That is my review of the headers i will hopefully be getting a dyno and some track work, hope this helps anyone who is considering the headers.