a, a2, b , c , whats the biggest?

[boatermike]

impellers , confusing, would a c be huge or tiny?

[Propless]

Basically a C impeller takes less power to turn than an A2 at the same rpm, because it moves less water at that rpm. You want to match your impeller to your motors power curve. If you motor makes a peak of 300hp at at 4300rpm you would want an A2, If you motor makes a peak of 300hp at 5900rpm you would want an E impeller. Wherever you motors power curve crosses the impeller curves on the graff will be your max rpm, A high rpm small block that builds 500hp at 7000rpm might not be able to turn an A2 impeller past 3500rpm.

http://i239.photobucket.com/albums/ff97/propless/Daytona/untitledyt.jpg

[boatermike]

excellent explanation thank you very much