You would be looking at the difference between the SCi and Si kits. They are rated for producing different amounts of air flow (cfm). The bearing case and general overall dimensions are the same but the impeller and volute design are much different. The Si operates at a much higher efficiency and is far superior in impeller design. As far as HP, both kits are under rated in my opinion and any modifications will only help your ultimate HP goals. The SCi is a great entry level kit but really doesn't leave room to grow. The Si is a very versitle blower and is more than capable of laying down 600rwhp with the correct supporting components. If you wanted an idea on a kit pm me and we could go over some of the options. Full kit vs standard kit and sci vs Si etc
