What is impeller pitch? And how does it really affect my skis performance?
First, it is important to understand the difference between varying impeller (jet skis have impellers) pitch and single propeller (boats have propellers) pitch. The differences are in shape and curve of the blades.
If a propeller has a pitch of 19, the pitch is the same along the entire curve of the blade because the blade has the same angle the entire length of the blade. Due to the shape and curve of an impeller, the angle varies from the top of the blade to the bottom, and therefore you will see different pitches like 13/18 or 16/21. This is called progressive pitch.
The definition of pitch is a movement measurement, not a size, shape or contour measurement. It is how many inches the impeller would move through the water during one revolution, assuming perfect, consistent water conditions (no foam or bounce, etc.) and therefore no slip.
Impellers are very inefficient, but that level of efficiency changes from one brand or style to the other. The size of the impeller does not change, the fit of the impeller in the jet pump housing remains constant. The shape and curve of the blades do change, and that is what changes the pitch numbers.
Hence, a stock impeller for a particular ski might be a 12/18, the “equivalent” Solas brand might be 11/15 and another brand might be 14/22. The confusion often caused by these different pitch numbers is that it is too often thought that each of these pitch numbers relate to speed, when in fact they are all going to be VERY VERY close in terms of top speed.
True impeller effective pitch is a formula. PitchXprogressionXrakeXbladeangleXhubflair.
Any difference in one of these will affect the overall pitch. Considering this, you CANNOT compare pitch from one impeller to the next.
You really don’t have choices. You go to the chart for each brand and model of impeller and it tells you which impeller to use, and it shows only ONE choice. That is the one you run for best top speed AND best acceleration for that pwc and impeller. Any other choice is going to be a compromise, and might cause engine and drive damage.
This is not to say that there is not a difference in impeller brands and quality. There most certainly is. It is just that the difference is not in speed.
The differences are in:
Agility – You can feel the differences in a high quality impeller in your turns.
Propulsion – A quality impeller will reach top speed much quicker and more smoothly.
Handling – You will feel an overall improvement in the way the ski runs.