i have an 07 TRX450r with an HRC kit, whats the best pipe to use with the header that comes with the kit?

 

The fastest 450 I know of (kicks everybody's butt at the Glamis drags), has nothing but an HRC kit with an uncorked stock exhaust. I know the stocker isn't very sexy, but as far as performance I don't think any of the aftermarket ones are going to net you significantly better performance, although they may be a little lighter.

I am running an FMF PowerBomb header and Factory 4.1. If I was doing it today, might go with the MegaBomb and Q....to keep the noise down.