Have both 97' 550 cougar the 550 is smooth running and clucthing is great. The 94' 580 is in a EXT mountin cat starts first pull drinks to much oil but a constant runner this motor sounds loppy and seems to make its power on top. i notice i trail ride the 550 smoothly at 1/8 to 1/4 throttle now the 580 same thing but blip the gas more as it's more of a choppy **** down low. the clutching on these is red spring primary and yellow secondary. helix are different i assume. is this the difference a 580 made a crappier ride i see no power inprovements in the 580 nil to none. anyone chime in on this im wondering if my 580 timing is off or i have play now the 550 is 135psi both side's 20hrs on new SPI's the ext had a top end stock pistons 2 years ago we have also had almost no snow in the past 2 years so id say 80 hrs on this top end and still 135 both sides. considering these motors share bottom ends 580 runs odly different to me.