For GPM, let's grab the Kalkalata again. to do a very rough ballpark guesstimation...
Due to direct drive, when the Engine rotates 6000 rpm, the Pump also rotates 6000 rpm (it better!
). So need to find amount of Water processed in ONE Revolution and multiply that by rpms to find gpms.
Also need Pump Volume in Gallons. So, a SJ Pump measures 144mm Diameter and is about 3 inches long. Same as Volume of Cylinder so:
Pump Dia. = 144mm = 5.7 inches. Pump Area = 3.14 x (5.7 x 5.7)/4 = 25 sq. in.
Pump Volume = Base x Height = 25 sq. in. x 3 in. = 75 cubic inches. *This is maximum amount of Water that can fit in the Pump without an Impeller*
Converting to gallons,, since 1 cubic inch = 0.004 gal, then 75 cubik inches x .004 = 0.3 gallons is the most that can fit in the Pump Space w/o an Impeller.
So for every complete revolution, 0.3 gallons of Water max can flow thru the Pump. In a sense, the Impeller acts as a Throttle Valve, "fully opening" each revolution.
But the Impeller has 3 Blades or "Paddles", so the Pump is actually moving/sweeping 3 times the Pump Space Volume.
So each Minute, 3 x 0.3 gallons flows thru the Pump. Then actual flow rate is about 0.9 gpm.
At 6000 rpms, 0.9 gal/rpm x 6000 rpm = 5400 gallons max processed per minute = 90 gal per second
To check, let's see how much Thrust is produced by 90 gal per second.
Gallon of Water weighs about 8 lbs, so 90 gallons weighs 720 lbs or Thrust is about 720 lbs per second.
This is ballpark to the 550 lb Kaw 750 SX Thrust rating spec'd by Kawasaki.
Also, since Jetski Pumps are not loaded perfectly and the Intake water is aerated aka "dirty" or foamy, the use of a one-second time window to calculate Thrust is not far from the real instantaneous Thrust number, which would be somewhat lower.
Any Pump Experts that can chime in and correct, support, confirm, deny, supplement or clean-up my getter'dun Calcs and Assumptions?
Every day is a School Day for me, so please comment and edumacate me...