Different motors same pitch

I have experienced something strange:
Two different motors with different gear ratio same pitch propeller same max speed that is: a Suzuki DT 65 - 65 hp 1.92 gear ratio 13 pitch propeller 36 NMPH
a Johnson 50 hp - gear ratio 2.8 13 pitch propeller 33 NMPH.
Both motors at 5200 RPM, on the same boat.
Now I've got a 90 hp Johnson, it came with a 19 pitch propeller and I wonder what will happen, haven't tested it yet?
Can any body explain is the pitch specific for the propeller only or it is related with the engine.

Re: Different motors same pitch

What boat?
Pitch is more specific to the application boat size weight and design and the typical load.Your props are probably different in design but the similar numbers cold be from similar designs or from dissimilar designs.Identical prop sizes from different manufacturers may produce different results.You have a pretty good difference in ratio. The Johnson diameter is about 1 inch bigger.Thats not the same speed.The speed difference seems about right for probably basic setups.Motor height can make a big difference in performance.The 19 is a good starting point for the 90.You can select a prop based on the specs you get on the water.

Re: Different motors same pitch

What year Johnson 50 are we talking about? If its anything built in the last fifteen years or so it does not have a 2.8 gear ratio - it has a 2.42. Engine gear ratio is determined by a number of things. Engine displacement will ultimately determine its torque characteristics which dictates gear ratio selection and therefore the range of prop diameters and pitch that the engine would be able to twist. Propeller RPM (not engine rpm) determines the ultimate speed of a boat. Gear ratio ultimately determines engine rpm with any specific prop. It's all a numbers game. Merc 50 2-strokes run a 1.83 gear case but the props are small diameter with less pitch than a 40/50 HP Johnson/Evinrude that run larger diameter props with more pitch. The net result is the Merc prop spins faster and with less pitch but will run the same speed (theoretically) as the larger J/E prop with more pitch running slower prop rpms. But hull design and engine setup, state of tune and a host of other things, including prop design all enter the picture. As was pointed out, two 13P (or any pitch) props from two different manufacturers may not, and generally do not, perform exactly the same.

Re: Different motors same pitch

I have a 19 P on the motor will test it, I mainly use the boat for waterskiing:
that is I need a little lower pitch propeller, I ll have to be careful with over revolution with me it's OK, but whem my son gets the boat no one knows
well time will show. Theory always varies in experience.
Thanks