HKS is very quiet, until you go WOT and its really loud then, but it should be at WOT

 

I haven't seen anyone over 500-550 rwhp with the HKS though... I'm think if I really want to do something, why not add 3" exhaust cut outs to the end of the APS test pipe? Tie it in to only open at say 14 psi or higher via the Haltech - hmmm we'll see if the need for speed continues to grow or not