My manual states a range of 5000\6000 for the 25 hp version 5150-5850 for the 30 hp. Same block for 30 just no carb restrictor plate. Stock 3 blade 9.9x 13 tops out at 5000 rpms at the moment. I just got a new stainless power tech 4 blade 10 x 10 cupped. I plan on raising the motor but for now if rpms are any lower than 5000 will it cause any strain on the motor running that far below max rpms? I'm hoping speed and rpms won't suffer drastically from current numbers since I'm dropping from a 13 pitch down to a 10 although adding an extra blade
I'm running a 15p on my 25 with an extended and increased cup down the blades. I dont know what pitch that makes it after I had it cupped, though.
If you are running at least 5K you will be fine, any lower than that and you need to correct it as soon as you can because yes it can cause a strain on the engine. Adding cup to the trailing edge increases pitch, adding cup to the aft will increase rake. Since you dropped 3" you probably will be fine in the RPM range.
