No flap for me either. Free weight loss and in my opinion they restrict snow evacuation forcing the snow to go back through the tunnel creating more resistance for the track. I have a bdx bumper setup and flat cooler on my 07 M8 w/powerclaw track and also on my 07 M1000 w/attack 20 track and have never had any cooling issues. Haven't had any problems on the 10 HCR either, but only 5 rides on it.Granted I'm in good soft snow most of the time.
