In order to install a lightweight pulley you need to cut the A/C belt off, so u would have to buy a new belt and the belt comes with the tool to install it from subaru. there is no need for the tensioner. I have not been able to price the 2008 belt but it cant be that expensive compared to a $60 tensioner. the new A/C belt is not desighned to be used with the tensioner from the old model. Did I answer your questionwhy would you want a new belt? are aftermarket ones superior? or is just cheaper than buying the tensioner?
(im assuming you havent worn your belt down already...)
Sorry for the late response. The OEM belt comes with the tool to install it, so the only way to gois OEM. The bad news is the stock belt is $98 because of the tool. I havent purchased the belt yet and the crank pulley is sitting next to my PC. Race season has started up so I have been watching my money the good news is my hand is broken so I havent had to dish any $ out yet, the bad news is my hand is broken and my bike is sitting in the garage needing soime TLC which means money for it.sorry to nag you again but which belt did you buy? just order an OEM one?