I have one, few tanks old, still breaking in and still amazing me the torque and smoothness. Opened the muffler a bit but no added port. It gave the trigger more response for sure. So smooth they feel slow which they are not. Stock to stock I had a new 390 and sent that down the road. Ported of course the 390 will wring the 576's neck but out of the box the 576xp is just a very nice saw. Great price too. GLWS.