OEM 155 Pump Talk

[JetManiac]

Here are some comparison pics of 144 and 155 pumps that should help. The 155 wear ring is longer, but the mounting ears on the 155 reduction nozzle were moved forward so that the overall bolt spacing is the same even though the 155 overall pump is longer.

 

[WB1994]

Big hubs reduce internal volume so the inside of the pump can fill and prime faster. This theory is for any pump diameter. Bigger pumps give better hole shot or bottom end power and will reach the same speeds but doing it with less pressure and more volume. To a certain amount. Eventually to get higher speeds you will need more hp to power the pump to higher pressure, or go down in pump size and setup the smaller pump to create a higher spped pressure at the loss of some bottom end. Pumps are very tuneable.

Yes Its obvious that a stuffed pump has less volume so its quicker to fill with water. Not sure where your going with that but it looks like you agree that greater volume equals greater movement of mass. Which in turn woulld mean stuffing or bighibbing a ump is counteractive tolow end needing freestylers . No?

 

[D-Roc]

When you change the internal pump volume I think of it as the timing of the pump. It's not so much as priming faster in seconds but more of rpm from engine. The less internal volume (short tail cone) the slower it primes and pressurizes this happens at a higher rpm on the motor end. On weak motors it would help get the motor onto the pipe by letting it rev up a bit longer with less load, then you would get your "blast" in the powerband. If you cannot adj you pump to the motor then your setup will only work so well.

 

[D-Roc]

It's always going to be the magic sweet spot ratio of pressure and volume by a given prop pitch. Tuning by the tail cone volumes and using big hubs in combination with reduction nozzle diameters is how you get your pump to respond well to rpms and your engine power delivery.

 

[WB1994]

It's always going to be the magic sweet spot ratio of pressure and volume by a given prop pitch. Tuning by the tail cone volumes and using big hubs in combination with reduction nozzle diameters is how you get your pump to respond well to rpms and your engine power delivery.

Your kind of getting all over the place . What does prop pitch have to do with pump volume? And doesnt it litterally take a split second to prime a pump no mater cone size or stuffer or whatever? So im not understanding your theory of it being your "timing" of a pump. Its really not much volume difference we are talking about here ... maybe 1/100th or less of a volume differance?

 

[D-Roc]

Prop pitch is like the gearing. Not much volume difference in cylinder heads either but a few cc's makes a difference. Now try compressing water. If internal volumes makes no difference why would we have different tailcones to help change internal pump volume. Why does a slight prop repitch make a difference? What part of pump timing vs engine rpm do you not understand?

 

[D-Roc]

Prop pitch = water speed vs rpm. I think of that as gearing. The internal volume I try to change to help adj at what rpm the pump primes and is pumping. (Rpm at which the prop is no longer slipping. ) reduction diameter I think of as the compression and how much load and back pressure is best for the prop pitch. The veins and the number I think of is how quickly the water can be processed at a given load. Pumps are pretty complex and I don't fully understand all of what is going on. I just try to make sure I have as much adjustability to help correct what I did't get perfect. Alexhockey 14 vein 155 pump makes me know that a 155 diameter pump can work even better than my oem setup. I do plan to see if I can get a bit better pump responce by going down a bit more on my reduction nozzle. After riding his ski it makes mine feel like I am slipping a bit more than his. Not sure if it's his 8 extra veins or not.

 

[DAG]

Probably going to OT my own thread but I'm curious if any of the old Yamaha/Kawasaki development engineers are on the jap forms laying out the tech Q&A details. It sure would be nice to understand how/why things work better than the jibber jabber we post all over the place. We assume so much stuff but I guess that's all we have... Can we get a fellow to join the forum for Christmas? That's my only wish

 

[kevbo]

I measured my jet stream at 70mph. This is not a very effecient way to make thrust at low hull speeds. More low speed thrust can be made with the same power by trading some of that pressure for volume. Adding stator vanes reduces backfilling behind the impeller blades. This becomes most important when there is a lot of air in the water. Large hubs fill a dead area that otherwise holds circulating water and air. The compressed air within the pump expands and blows water out the front whenever the inlet stream is interrupted. The pump cannot reprime untill intermal pressure drops.

 

[D-Roc]

That's a better explanation of what is going on. I am not good at explaining it. I have not been able to test setback vs non setback pumps back to back to see what difference that makes on pump loads or thrust speeds. Any input on that would be nice to hear.


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[D-Roc]

Probably going to OT my own thread but I'm curious if any of the old Yamaha/Kawasaki development engineers are on the jap forms laying out the tech Q&A details. It sure would be nice to understand how/why things work better than the jibber jabber we post all over the place. We assume so much stuff but I guess that's all we have... Can we get a fellow to join the forum for Christmas? That's my only wish

Pump tuning is a magic dark art.


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[DAG]

Pump tuning is a magic dark art.

Agreed. But that's just because collectivelly "WE" don't understand it as well as we should

 

[D-Roc]

And there are so many factors that effect it and the only test equipment on changes are by our test rides. Our data tends to be well you know, opinionated.


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[Little_Franny]

I measured my jet stream at 70mph. This is not a very effecient way to make thrust at low hull speeds. More low speed thrust can be made with the same power by trading some of that pressure for volume. Adding stator vanes reduces backfilling behind the impeller blades. This becomes most important when there is a lot of air in the water. Large hubs fill a dead area that otherwise holds circulating water and air. The compressed air within the pump expands and blows water out the front whenever the inlet stream is interrupted. The pump cannot reprime untill intermal pressure drops.

How? 70 mph? Couch? I'm curious now

 

[kevbo]

How? 70 mph? Couch? I'm curious now

This test was done by measuring static thrust on a Superjet strapped to my test trailer and sunk as deep as possible. I simply measured the nozzle area and thrust, then used a dynamic pressure calculator to get the speed. For full speed testing I plan to make a pitot ring behind the nozzle but havent had time.

 

[Little_Franny]

This test was done by measuring static thrust on a Superjet strapped to my test trailer and sunk as deep as possible. I simply measured the nozzle area and thrust, then used a dynamic pressure calculator to get the speed. For full speed testing I plan to make a pitot ring behind the nozzle but havent had time.

Very cool, measuring thrust with some sort of load cell?

 

[WB1994]

Prop pitch is like the gearing. Not much volume difference in cylinder heads either but a few cc's makes a difference. Now try compressing water. If internal volumes makes no difference why would we have different tailcones to help change internal pump volume. Why does a slight prop repitch make a difference? What part of pump timing vs engine rpm do you not understand?

You cant really compare cylinder cc, s to pump volume but yes just a few cc, s makes a big difference under preasure unlike the pump where your not compressing the water.

I never said internal volumes made no difference , I actually said the opposite . I was saying imo the susubtle differences in cone volume doesnt noticeably change how fast the pump refils to react correctly with rpms so your pipe hits just as your pump compleates the filling prosses. Too many other variables like whitewash that kills overthinking that.

You change tailcones in order to change pump volume ?

The prop is the biggest key to the whole prosses so yes a slight repitch makes a difference. You didnt really want me to ecplain why right. Just trying to answer your questions.

 

[D-Roc]

I was using it as an example of how a little can make a big difference. Yes I use my tail cones to change the pumps internal volume behind the prop. If a pump is not compressing the water to create pressure what does it do? You seem to know more about it than me so enlighten me if you don't mind. And yes please explain the prop pitch.


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[DAG]

Stop Pet Peeve: The term "compressing water" been stated several times now in this thread. There is no way water density changes in our dinky little pumps. Pressures, Force, and Area should be the terms we use to describe whats going on. Ok carry on

 

[D-Roc]

I agree that the water does not change density but if you pull it in thru a 155mm opening and force it out a 90 mm hole it will create thrust or pressure. It does not compress so when you change your exit diameter by even 1-2mm it can make a big difference on engine load or if your prop will slip. That why I said try compressing water, it doesn't compress very well and builds pressure quickly.


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