I have had Holley 600's vac. sec., 750 vac. sec., Carter 625's (actual Max Wedge carbs), but now have a set of old Holley 660 Center squirters that have been reworked to like 690's. They are by far the best running set I have had on. More lower end response and the top end is unreal. They are on a Weiand tunnel ram that has only been port matched top to bottom and port matched to the heads. Also running just old cast iron heads.