“This is our 2011 spec exhaust. The bike changed a little bit, so we change our exhaust. We have added the PHD chamber (which is what we call the resonance chamber) to some the exhaust systems in our line. Depending on the bike, the PHD Chamber good for one or two decibels of noise reduction, a little more throttle response off the bottom and a stronger pull through the mid. The PHD Chamber will only be available for select applications. The applications that didn’t see a real benefit from the PHD in our development and testing don’t get feature in production. Doug isn’t into gimmicks or trying sell pipes based on unnecessary features.

The Doctor has a PHD. DR.D calls their resonance chamber a PHD Chamber.  

“The part number for this pipe is 7247, it’s a stainless steel and aluminum system and retails for $619.99. Even though we added the PHD Chamber to some systems, we didn’t increase the retail prices. Plus, we have a 20 percent off promotion going on right now for the holiday season so it’s a really good deal.”-DRD’s Mark Tilley