X4 prop selection

[csmelone]

I am working on my senior project at Worcester Polytechnic Institute. We are using a 1997 spx hull with a special power plant with specs as follows:

Max rpm: 7500
70 hp
116 ftlbs torque

Stock pump will be used. I was thinking of using a prop off a 1994 spx only because it would be easier to source given our budget and time frame, instead of a custom pitched prop. I know the 94 spx hull is not an x4 but I'm afraid a prop off a 95 xp will put too much load on the motor. I am not sure if its the same size pump or if it will be best for low end torque either. Any suggestions or experience would greatly appreciated. We are working on a very tight budget and timeline. I was also thinking of impros. I already tried contacting them but have not heard back.

 

[mikidymac]

That impeller is going to be way to short due to your higher horsepower and rpm.
Since you have very high torque and high rpm I would thing you would want a taller impeller.

Honestly your best bet would be to call Glen at Impros. He used to be the Skat-Trak guru until he bought Impros. If anybody would know it would be him and since it is for a college project he might even help you out.

 

[csmelone]

That impeller is going to be way to short due to your higher horsepower and rpm.
Since you have very high torque and high rpm I would thing you would want a taller impeller.

Honestly your best bet would be to call Glen at Impros. He used to be the Skat-Trak guru until he bought Impros. If anybody would know it would be him and since it is for a college project he might even help you out.

Do you know the best way to get in touch with him? I've already tried the contact info on their website with no luck. Would a stock prop from a 717 x4 be tall enough without putting too much load on the motor? Not sure how big of a difference the pitch makes for something 70 vs 85 hp. We have a fast approaching deadline so I'd rather order a couple props and swap them out rather than waiting for one to be re-pitched. Just not sure what the best option would be. Also I forgot to mention the peak power can come on as soon as 3500 rpm but we can easily adjust the curve and have peak power come later in the rpm. What we are building has never been done before so it is a lot of trial and error, just looking for a good baseline to start with for testing.

 

[Whus02]

It's hard to give an exact recommendation with the details you've given, and even with all of the details of your motor, I doubt there is comparable pwc powerplant that would aid in prop selection. With that said, a 717 x4 prop should be pretty close, and you can re-pitch impellers without sending them out (within reason, of course).