So, if power assist is the name of the game then big pulley- small swept volume would be the best combo for reducing parasitic loss. Yes? Steve Avery Date: Wednesday, May 4, 2005 08:03 PM From: Tom Jennings <tomj@xxxxxxx> >> Does the larger diameter of the pwr strng pump assembly equate to being >> underdriven compared to the Eaton set-up? Does it use less hp to drive >> the Saginaw assembly with the larger diameter pulley?? The vane type has a larger swept volume; low RPM moves a lot of fluid; big driven pulley rotates slower. The roller type doesn't move so much per rev, so more RPMs; little driven pulley rotates faster.