The pump discussion thread

[WFO Speedracer]

Ok I know that jet skis are basically just engine driven water pumps, and that the larger the pump the more water it will move in a given time span if the engine has the appropriate amount of power to push it.

My question is this given a platform such as a Superjet and all other things such as engine HP being equal between two different skis what kind of difference will you see on the ski with the bigger jet pump. Increased top end speed, more bottom end thrust , what exactly ? Engineers feel free to chime in here.

 

[SXIPro]

You should consult 800Doo on PWCYesterday for all pump questions. He is the engineering guru in that regard.

 

[kevbo]

Bigger pumps have some advantages at modest rpms but there is more to it than just size. The inlet and the prop have to be maximized in order to realize enough of a gain. Thats where jetskiers drop out, we can buy bolt-on parts and thats about it.

 

[MNTURBO]

Well I am no expert, but I have ridden a FX-1 with a tiny 122mm pump and an FX-1 with a 144mm pump

The small pump can't offer the immediate response you get from the 144mm pump, but it does surprisingly well on the top end

 

[FlightPlanDan]

This may be useless....you know way more than me. But I have personal experience with pump mods.....that make it worse.
Yamaha and Kawasaki pay engineers a lot of money.....
There is a reason they made the thing the way they did. I'm not talking about a new impellor....

It's a tunnel with a propellor inside.

You can change the way the water flows thru and gain or lose. Aluminum pump shoes are a good example of a mod that can help or hurt depending on your attention to detail.

 

[WFO Speedracer]

I know the difference between the 440 pump I had in the 300SX and the 650 pump was drastic, more top speed, more bottom end snap , just more all around. There are several model of sit downs where they have gone to bigger pumps with the same engine, the Waveventure 701 Waverunner XL 700 is one of them, I have never had the opportunity to run both skis back to back though.

 

[FlightPlanDan]

It is interesting...although I and many others don't have the means to play too much with the pumps, I would be enthralled to hear results of experiments from those of you "in the biz" that might have different options laying around the shop.

My previous post was based only upon the super jet.

Again, other than MAG pumps, maybe a bit more attention is due in this area!

Good thread!

 

[sportfish258]

I'm with you weedoo . I never fully understood how all that pump stuff works pressure v/s flow etc . I think we can all agree that the polaris base motors are arguably putting down the most power in stand ups today . I think Malone uses a 145 Kaw mag in his stuff. I may be wrong .

 

[IKSTEJ]

Ok I know that jet skis are basically just engine driven water pumps, and that the larger the pump the more water it will move in a given time span if the engine has the appropriate amount of power to push it.

My question is this given a platform such as a Superjet and all other things such as engine HP being equal between two different skis what kind of difference will you see on the ski with the bigger jet pump. Increased top end speed, more bottom end thrust , what exactly ? Engineers feel free to chime in here.

I'm not sure I'm answering the question, but
the goal is to process as much water as possible using the maximum size pump/prop combo the engine can drive at the right time, the desired rpm.
so putting any 144 Mag setup on our 1000 is like giving a whale a Tic Tac
put the right 144 combo on 701 to say 865cc and your at least in the ballpark
Theres a lot of tuning and adjustments to be made around it to get the desired effect, and correct performance
you bore the nozzle or use a smaller prop to loosen up it up for bottom end, & opposite for Top end.

whatever you do to one end effects the other.
If your not tuned right, what should be your optimum pump setup will feel overpumped
Its not easy to balance it all, and requires attention to detail.
(if anythings off anywhere in the tuning) what works for you may not work for your buddys exact setup, (pipe, carbs, ignition)
that includes the accuracy and condition of each component used.
Its easy to bolt parts up, not always so easy to get them to work in unison.
thats why its a good idea to follow your builder/tuners formula.

to a musician its like finding the "brown sound"

 

[cdickski]

The answer to you question is not as simple as bigger is better, or a bigger pump makes you ski go faster. From an engineering standpoint I would break a ski into several key components: The powerplant (engine), the intake area to the pump, the impeller, the fixed veins in the pump, and the nozzle.

Since you mentioned keeping the powerplant the same, the intake area in front of the impeller collects water and directs it into the pump/ impeller. While most people don't think of it this way the area in front of the pump is actually a nozzle preloading the impeller.

The impeller is a key component any definitely is not the same between differet sized pumps. It is key to match the impeller to the pump and power plant. A larger impeller of the same pitch will always handle/use more power than a small diameter impeller of the same pitch assuming the impeller are the same series and manufacturer. That said if the engine produces exactly the same power it is safe to assume that as the pump gets bigger, the impeller pitch would need to drop to kep the engine loading the same.

The fixed veins help accelerate and straighten the water flow prior to the nozzle. The center hub diameter ends up taking up space which changes the area/volume between the impeller and nozzle. That is the idea between pump cones to change the volume that water can fill and the direction it is moving prior to the nozzle.

The nozzle forces the water to accelerate and turns the moving water into meaningful thrust that propels the ski.

Getting a ski to do what you want is really about optimizing each component/system. Unfortunately they are all related, You initial assumption of the engine making the "exact same" power is flawed. The engine can only really produce as much power as the pump can handle. The pump acts as a fluid coupling to the water. If you got two different pumps to load the engine in the exact same manner, the work into the pumps was identical. It would pretty much come down to the efficiency and matching of the components. If the thrust coming out of the nozzle is the same across the board rpm and boat speed between two different pump setups you have pretty much two identical pumps.

From my personal experience a small diameter pump like a stock FX-1 sacrifice water volume in exchange for higher pressure works well at high speeds. A bigger diameter pump develops lower pressure to keep the HP the same, pair that with a big nozzle and you'll get great low end punch.

Unfortunately probably the most important thing to consider is cavitation. Air in introduced via the intake nozzle, or water boils in pump and the fluid coupling breaks down before the nozzle. If every thing doesn't work before the nozzle there is no thrust that makes our skis go.

I am sure the stock FX-1 pump setup looked great to engineers on paper and I am sure sure than there are plenty of members on here that will tell you ow great a pump swap is. While not commonly done I personally think it comes down to building/tuning the pump to match the boat and then making the power for the pump.

 

[FlightPlanDan]

That is a really good argument "not to deviate" for an "all purpose" ski should stick with the stock engineers.

But, some are willing to sacrifice top-end (for example) to achieve a bigger hit at the bottom....

Racers want the mid and top...

We know that there are different motor set-ups for these "wants".

What I think this thread is working toward is pump mods and or completely different pumps for specific purposes.

 

[Dustin Mustangs]

The answer to you question is not as simple as bigger is better, or a bigger pump makes you ski go faster. From an engineering standpoint I would break a ski into several key components: The powerplant (engine), the intake area to the pump, the impeller, the fixed veins in the pump, and the nozzle.

Since you mentioned keeping the powerplant the same, the intake area in front of the impeller collects water and directs it into the pump/ impeller. While most people don't think of it this way the area in front of the pump is actually a nozzle preloading the impeller.

The impeller is a key component any definitely is not the same between differet sized pumps. It is key to match the impeller to the pump and power plant. A larger impeller of the same pitch will always handle/use more power than a small diameter impeller of the same pitch assuming the impeller are the same series and manufacturer. That said if the engine produces exactly the same power it is safe to assume that as the pump gets bigger, the impeller pitch would need to drop to kep the engine loading the same.

The fixed veins help accelerate and straighten the water flow prior to the nozzle. The center hub diameter ends up taking up space which changes the area/volume between the impeller and nozzle. That is the idea between pump cones to change the volume that water can fill and the direction it is moving prior to the nozzle.

The nozzle forces the water to accelerate and turns the moving water into meaningful thrust that propels the ski.

Getting a ski to do what you want is really about optimizing each component/system. Unfortunately they are all related, You initial assumption of the engine making the "exact same" power is flawed. The engine can only really produce as much power as the pump can handle. The pump acts as a fluid coupling to the water. If you got two different pumps to load the engine in the exact same manner, the work into the pumps was identical. It would pretty much come down to the efficiency and matching of the components. If the thrust coming out of the nozzle is the same across the board rpm and boat speed between two different pump setups you have pretty much two identical pumps.

From my personal experience a small diameter pump like a stock FX-1 sacrifice water volume in exchange for higher pressure works well at high speeds. A bigger diameter pump develops lower pressure to keep the HP the same, pair that with a big nozzle and you'll get great low end punch.

Unfortunately probably the most important thing to consider is cavitation. Air in introduced via the intake nozzle, or water boils in pump and the fluid coupling breaks down before the nozzle. If every thing doesn't work before the nozzle there is no thrust that makes our skis go.

I am sure the stock FX-1 pump setup looked great to engineers on paper and I am sure sure than there are plenty of members on here that will tell you ow great a pump swap is. While not commonly done I personally think it comes down to building/tuning the pump to match the boat and then making the power for the pump.

^good post^



I think to answer this you would have to know every spec of the ski right down to how it's tuned and the conditions it's to be tested in. Putting in a bigger pump on one ski could have the exact opposite effect as putting one in a different ski. What determines the outcome is how the pump was sized, in relation to the rest of the ski, to begin with. I think this is a way more complicated question than most would realize.

 

[Freakrider]

I know someone that put a 155mm pump in a blaster 1 and it did not work well. He found out that the pump intake tunnel could not supply enough water like a B2 hull can...anyone agree with his findings ?

 

[Watty]

Just to throw something else into the ring. My engine builder advised me to use a 140mm mag pump on my 8mm/89mm Dasa PV engine. I'm quite confident that this will work great as the prop was supplied and pitched to his specs.

 

[kevbo]

I know someone that put a 155mm pump in a blaster 1 and it did not work well. He found out that the pump intake tunnel could not supply enough water like a B2 hull can...anyone agree with his findings ?

First understand that water boils at low pressure, after that the rest is easy.

 

[WFO Speedracer]

One of the many projects I have on the back burner is another Jet powered runabout boat, I have built one with a Seadoo 720 engine and pump, it does ok but really not enough ass to push that big ass boat. I am thinking a Yamaha 1200 NPV engine with a 155mm jet pump would push it fairly well.