This is a Powerbond Race/Performance 5% overdrive balancer. The increased size increases the speed ratio between the balancer and the supercharger pulley, which will spin the supercharger faster than the OEM balancer.
SFI Apprived to spec 18.1 and suits the full range of L67 VS-VY Commodore's as well as other similar platforms.
Image for display only, will also fit the Ecotec NA but it will need to be mirror balanced to your stock Ecotec balancer. Please note these may have slight marring on the balancer thread, tthis can be cleaned up if needed.