rpm to mph

# Thread: rpm to mph

1. ## rpm to mph

what is the rpm to mph lets say 6000 rpm with an A cut impeller and the same with an B cut and B/C cut

2.

3. Wait for Jon (Sleepercp) to chime in. He'll handle it.

4. HP vs RPM (charts and "numbers") is/are fairly "pathalogical" MPH will vary widely from boat to boat & set up to set up Tom

5.

6. You would need a degree in hydrodynamics to come up with a MPH at a given engine speed/setup...Besides, just because its an A does not mean the RPM would relate to any particular volume, cavitation, worn wear ring, intake inadequacies all would come into play.

Hull speed is determined by nozzle velocity and area (thrust) with the drag from the hull taken off the top...

Too much math for me...

GT

7. Originally Posted by 787chuck
what is the rpm to mph lets say 6000 rpm with an A cut impeller and the same with an B cut and B/C cut
Not fast or quick enough!!!!!!!!! you will always look for more.

8. Originally Posted by 787chuck
what is the rpm to mph lets say 6000 rpm with an A cut impeller and the same with an B cut and B/C cut
As stated lots of variables. At the same RPM the A will move more water but the B or B/C my well be quicker and the A may out mph them but it might take 1/4 mile to find out. BP298 will have a good idea I'd bet.

S CP

9. There is no specific boat to MPH ratio. the same model boat with the same motor will run a different MPH than its counterpart it is just the nature of the beast. Even with a hydrodynamics doctorate, the affect the water has on the hull as it passes through the water is everchanging depending where the boat is sitting in the water and water conditions. The only way to really figure out the MPH difference with different impellers is to change out impellers and map out the MPH.

Cy

10. Originally Posted by Sleeper CP
BP298 will have a good idea I'd bet.

S CP
nay nay... if you know what kind of boat it is, how much it weighs, how much hp it's making at what rpm, everything there is to know about the pump (what it is, what's in it, who did it?), a person can make a reasonable guesstimate that will be in the ballpark.
no way someone can say x rpm = x mph, solely based on impeller size without some idea of the rest of the package...

11. Originally Posted by bp298
nay nay... if you know what kind of boat it is, how much it weighs, how much hp it's making at what rpm, everything there is to know about the pump (what it is, what's in it, who did it?), a person can make a reasonable guesstimate that will be in the ballpark.
no way someone can say x rpm = x mph, solely based on impeller size without some idea of the rest of the package...
Sorry about that; I didn't finish my thought last night, Cold medicine and beer

Someone would need a baseline to work from then someone with lots of experience (like you) could make an educated guess.

S CP

12. Originally Posted by Sleeper CP
Cold medicine and beer

S CP

Right On!!!

13. ok so what is the def. and the performance gains and lose from one impeller to the next an A to B to B/C

14. Originally Posted by 787chuck
ok so what is the def. and the performance gains and lose from one impeller to the next an A to B to B/C
Chuck Once more all will be dependent on the boat ,the weight of the boat the motor ,where the motor makes power (power band) and what you want from the boat From what you've told me I'm not sure yoour not pretty close to "optimum" right now, good to chat last nite , enjoyed the nostalgia Tom

15. hay tom i know what your saying the miller is about done just picking some minds looking to do another one really want another lite race tunnel just looking to see where to go with it i always just gave the pump to papps and never asked why this impeller cut so im asking now

16. Originally Posted by 787chuck
ok so what is the def. and the performance gains and lose from one impeller to the next an A to B to B/C
ok, here's a very generalized answer.
if you have a pump at standard tolerance, you remove an A impeller, and replace it with another impeller with exactly the same measurements, except the vanes are cut to a B size, you should gain somewhere between 250-300 rpm. BUT, that is totally dependent on your engine's hp curve at the A rpm, and the B rpm... because, it's all about absorbed hp - how much hp is converted to thrust, regardless of impeller size.

as a very hypothetical example, say, with an A, your engine stops climbing at 5000rpm. but, your "peak" hp is 6000 rpm, and the curve indicates 6000 rpm is 70hp greater than it is at 5000 rpm. if the curve is linear, it "looks" like there is an increase of about 7 hp/100 rpm. so if you change out to a B, same model, make, everything the same except it's a B, you should gain 250-300rpm, which allows the pump to absorb approximately 21 more hp - converted to thrust. slightly greater thrust, slightly greater speed, quicker acceleration, and perhaps, slightly more than a 300rpm gain. the same concept applies to b/c, c, or d... it's all about the hp curve, and how much additional thrust can be developed at a higher rpm.

again, this is a very generalized answer to your question. there are many many curveballs, as in what if you did this, what if you did that, that can alter the standard answer.

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