How Much Diffuser Ring to Cut Off?
 

I have a pair of labbed P5Xs (31s). Would still like to get some additional rpms. Should the diffuser ring be cut off? A portion cut off? Or, look for another place for rpms. Right now planing is not an issue. Looking for 2-3 hundred rpms.

I've heard that the rpm gain of cutting off the diffuser ring is 50-100rpm.

Griff is correct. We often see even less with the Hydro.

why is it typically cut off ? And what is its purpose ?

Slight speed gain and may slightly reduce bow lift. It can make getting on plane very difficult in some cases.

RPM gains to be followed by mph gains.

Actually the reduction of the diffuser can increase bow lift. Planing is the key issue.

Brett - I sent the props off today. After talking with you, I decided to have it done yet this fall. I left a note in the box to check my file. We spoke of the difuser ring along with some other modifications.

Thanks, Brett. Let me know if you find anything else that needs to be done.