Freestyle Optimum Intake to pump size?

[CARBONX2]

As the title says I wonder if there is an optimum Intake gullet to pump size, as I see 155mm pumps getting fitted to skis with smaller and smaller engines. Is it only for easier drawing in of the water by the pump, does water 'storage' play a role?
The Wabuzun and UltimaX hulls seem to have about 240mm wide gullets and I guess 155mm - 160mm pumps.
Anybody that has done testing care to respond?

 

[djraider700]

Im no expert on pump design but I would assume a larger intake gullet would help store a large amount of water for immediate low end throttle. The large pumps with high power motors would require the extra water for the best punch off the bottom. At higher speeds it seems it would become less efficient because you would lose some velocity to the incoming water. Intake/pump size ratio could be further augmented with different impeller pitches.

 

[CARBONX2]

Purely looking at flatwater freestyle
The larger gullet means less hp to draw in water to pump.I am thinking the larger pump uses the lower pitch to move the water a shorter distance per revolution but the extra diameter makes up the volume to give the same or more thrust. The less distance moved for the same thrust gives thrust for longer as it takes longer to empty the pump, this combined with more stored water in inlet also adds to longer thrust duration.

 

[kevbo]

All pumps require some head pressure for maximum efficiency. This is a problem for standups since the pumps run close to or above the surface. Oversize inlets collect more water at static and low forward speeds. My testing has shown that thrust increases as the ski moves forward or when the pump is sunk deeper. It is typical to make 70+ psi behind the impeller but you can only go negative 14.7 psi (atmospheric) at any point in front of or over the blades before water boils (cavitation). Larger inlet to outlet ratios with flatter blade angles are required whenever head pressures are low in order to prevent cavitation. V-bottom sitdowns can get by with smaller inut and steeper blades without boiling water.

 

[MASSEY]

^ This Guy!

 

[CARBONX2]

Another thought today: Will the largest pump(with suitably sized intake duct) with the lowest available pitch impeller and the tuning done by means of nozzle and cone sizes give the best thrust?

 

[kevbo]

Another thought today: Will the largest pump(with suitably sized intake duct) with the lowest available pitch impeller and the tuning done by means of nozzle and cone sizes give the best thrust?

That is exactly what Yamaha did with their xl700 three seater, put a big pump behind a small engine. I abandoned the idea for small engines because these, in front of 144s, are requiring very low pitched impellers. A large custom engine with a dry pipe has already demonstrated superior results with larger pumps. From a technical standpoint we dont want to increase thrust by adding pressure because power requirements square against the results. Increasing thrust through higher volume at same or lower pressure is more efficient and follows power in a more linear fashion. Basically more thrust per HP at low speeds.

 

[CARBONX2]

Well a WB760/XL700/etc pump system(155mm) would be the cheapest bang-for-buck then(some of them also have trim that could be modded), add a Skat 7/14 and you have a 'good' pump. The biggest hassle is resizing the intake gullet if it is not already 160mm+ wide.

Or in the matter of my 146mm Kawi Skat pump in my ski, I should change the 13/18 to a 9/17 and tune with cone and nozzle again

 

[kevbo]

The goal is to set the pump so that the engine can reach maximum horespower rpm. Too much load makes low speed response sluggish and too little makes acceleration decrease as speed is gained. There is about a 100 rpm window where max overall performance is realized. Outside of that a compromise between high and low developes.

 

[#ZERO]

The Wabuzun and UltimaX hulls seem to have about 240mm wide gullets and I guess 155mm - 160mm pumps.
Anybody that has done testing care to respond?

Those hulls will work with pumps 140mm to 160mm in diameter and they even angle the engine & pump downward to help with stuffing the pump immediately after splashdown.

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[D-Roc]

I run a 9/15 in my 155 pumped superjet. I have a 771 pv 7 port dasa. I love it.

 

[Matt_E]

D-Roc, what's the biggest difference/improvement you noticed coming from a 144?

 

[D-Roc]

It's the pump response to throttle. The ski responds to rpms a lot better. The volume of water it moves works faster at moving the ski in the bottom and mid range than what less volume at a higher pressure can. The jet blast is large. More water pushing against water instead of pushing the water out of the way of the jet blast? Not sure if that last sentence made sence. Basically I think the larger jet blast is pushing against water behind the ski, closer to the rear of the ski, rather than a thinner jetblast that is pushing back against water deeper away from the ski. (Piercing the water) My top speed is down a bit but I still can hang with all my buddy's skis with 144's at wot. They may have a higher top speed but not by much. I know the large pump intake is causing drag at top speeds. It's Not pitched to flow enough at that speed/8500 rpm.

What does this mean? I dunno but I can get more air off of any wake or wave or swell than I could with my 144. Same hull/motor. More water volume and ski weight but using less pump pressure.

 

[Matt_E]

Hey, that's exactly what I am after. I know larger pumps trade top end for bottom end, but y'know, I was approaching 60mph with my 148 pump and that was way more than I actually need or use. So I am fine with losing some topend if I can get more violent bottom.
Thanks for the info.

 

[vshockey10]

D-Roc are you running a 155 mag or a 155 stock yamaha pump?

 

[CARBONX2]

I have been trying to figure out if the pumps are lower than the flat(centre/bottom) of hull or the chines have been raised?

Those hulls will work with pumps 140mm to 160mm in diameter and they even angle the engine & pump downward to help with stuffing the pump immediately after splashdown.

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[#ZERO]

I have been trying to figure out if the pumps are lower than the flat(centre/bottom) of hull or the chines have been raised?

The pump intake tract is sitting lower because whole engine & driveline assembly appears to be angled down a few degrees. You can see in the pic that the front engine mounting points have been raised up slightly and the bulkhead is slanted backwards. This setup would probably work well with the Yamaha 65V and 63M-LS reduction nozzles because they are angled upwards five degrees to compensate for the pump being angle downward.

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Around 1:20 in this video you can see some better details of the pump area and the chines.

 

[D-Roc]

I am running an oem 155 stator and wear ring. I blueprinted the pump a bit but more grinding was actually done to fit my tbm pump stuffer. This gave me a big hub so I got a e-75 skat swirl. Use my superjet drive shaft and rear bearing. I run a skat adj gp1300 reduction nozzle, gp1100 trim ring and an fx140 turn nozzle.

 

[D-Roc]

http://youtu.be/OIf39uy4GYE

 

[vshockey10]

Wow seems you went at the intake track also. nice work. That jump video was sweet also