Octane props & cones, confusing a newb

[hugh jair]

so I am familiar with boat props and understand how re-pitching or re-sizing can change performance for specific uses but when it comes to reading all these posts about props and pitches i get completely lost, partly because unlike boats im not quite grasping the "fraction" style descrition of props ie xx/yy

i'd love if someone could explain to me what said numbers refer to which would in turn help me understand, and eventually pick the right prop for what i desire ie does the number mean the size diameter or the pitch angle of blades etc etc, does going up..or down affect torque,low end, rpm, top speed.

would love to learn this its driving me nuts.

and since we're on this topic, i understand that changing cones changes bottom end power or top end speed what im not quite getting is how exactly does the cone fit into the driveline equation..is it acting as a reducer or cause drag..how does cone size/shape affect performance.what if you had no cone at all??

i know how to use the search feature but you guys all talk tech about prop pitch etc..i then realized i dont understand what any of those numbers mean so how can i learn from what i am reading ;-)

thanks for educating me

 

[VXSXH20]

I will try my best to chime in on the Cone question. The Stock pump or stator cone was/is designed for best over all performace when matched to the prop pitch and engine output rpm. Switching out to a shorter cone ( which most will do in the freestyle tailored skis, Will let more water into the pump/stator cavity and there for compress more volume and push out/exit at a higher pressure or thrust when it passes thru the tailcone or exit nozzle. this configuration will typically yeild a more agressive " POP" or hole shot when hammering the throttle from a low speed or idle. however this configuration will cause a loss in top speed on most applications..
-This is where a Longer tail cone would come into play-when you want slighty hight top speed and often slightly minimal increased rpm. Neither setup will really affect HP but can slightly effect engine performance on the low end of things. -
You would have to have some sort of cone or else the water pressure would build up and most likley cavitate and boil in the stator section. Since the rear nozzle acts as a venturi the water pressure needs to be directed towards the exit nozzle and out of the pump. the cones will aid in the compression process and divert the flow in the correct direction. -Just my .02 on that . ( I , by no means am a engineer-We have Bruce "Wet-Wolf" Wolford for that! ) He developed and adjustable cone that will expand and retract on its own under various pump load conditions that will increase the out put and performace on the ski under power. I know we all know what a pump looks like but i found a pic for a look and to show how a cone/core sleeve streamlines the flow out of the stator section.




-Props ( Impellers to be specific! -i dont know what people always say Motors either-they're pronounced Engines..) Is a different subject that I too get lost in translation.
Call Art at Jetworks and he will tell you, Who, What and Why A prop has three blades and what metal foundry was used on what day..-Grab a Chair and clear your mind for an hour..



( Lastly A little write up I found explianing pumps in general..Not mine it was from a seadoo guy)

There seems to be a lot of questions about cavitations and what causes it? What can I do about it? Why does my boat loose power when I turn real sharp? Then, the most asked question, why does my engine rev up without the boat moving?

I’ve explained this to a few people but because it seems that most members have noticed it, I’m going to shed a little light on if in a thread.

A boat with an outboard motor uses a propeller to create forward thrust. What ever the speed of the propeller and what the degree is, determines the speed of the boat. A propeller “chops” at the water, digging its way into the water to push itself along its forward path.

A jet boats propulsion system has no comparison with an outboard motors principle of thrust, except that they both are sources of power. From there, it ends.

I’ve done my best to make a little drawing with paint (I’m not an artist, so bare with the drawing) to try and help explain the theory and principles of jet boat thrust.

An axial flow jet pump works more like a compressor. Water enters through the low pressure inlet and is compressed by the impeller as it moves past the stator and into the nozzle. The low pressure inlet is always larger in square inches of space than the outlet nozzle.

The stator has a main purpose that most may overlook; probably wondering what it’s doing in there. But the boat can’t run without it. If it were not there, the torque from the impeller (compressor) would cause the boat to twist to the right from centrifugal force. The stator has a very aggressive blade design that almost completely reverses the direction of water flow. By changing the direction of the flow, it stabilizes the water for even output, removing the centrifugal force of the impeller. But more importantly, by changing that direction, it increases the energy of the fluid movement.

The last part of the pump is the diffuser. It’s that little vertical blade you see when looking into the pump from the back. It’s designed to remove any rotational force left over from passing through the stator.



At idle, the impeller (compressor) is completely submerged and while maneuvering in no wake zones…water is sucked into the impeller through the intake grate and gently compressed for a small amount of thrust.
But as the engine is given more power and begins to move onto plane, the pump is literally lifted out of the water and the compressor is being supplied with high volume, low pressure water, which is then compressed at higher rates as it moves through the nozzle. Without the wearing rings close tolerance, the water would lap over the outer edges of the blade and back into the low pressure side, where it would just do circles. The wearing ring, being within thousandths of an inch away, ensures that all the compressed water makes its way into the stator, to increase the thrust by changing its direction. The faster you go, the more pressure you put on the low pressure side of the impeller.

This principle of operation is very similar to the way a steam and gas turbine work. They have a several sets of rotating blades (impeller) and several sets of stator blades.

In comparing our pumps to a gas turbine on a jet airplane, if you were to change the size of the inlet to that compressor, only by inches, it wouldn’t get enough ram air to fly. The same is true with us. If you catch debris, like a ice bag left floating in the water, you’d lose all forward thrust. You’d find yourself under the boat/ski to pull that trash out of the suction grate.

So, in conclusion, when you are moving at WOT and do a sharp turn, the lose of speed equals a lose of pressure on the impellers inlet side, which in turn is going to reduce forward thrust till you straighten out and begin to regain speed.

If your sitting at a dead stop and slowly increase the throttle, then you will slowly gain speed, supposedly without cavitating. If you nail the throttle to 7k rpm, your engine is likely to hesitate while the compressor is given time to pump up the nozzle for thrust.

In my personal opinion, by a logical conclusion, I think the pure power generated by the 4-TEC’s and the 951’s would see less time in this loss of power just from the shear horsepower these engines create.

Any input or questions to this theory is welcomed. I hope I haven’t caused any/much confusion but after hearing all these questions about cavitating on start up or turning, I felt the need to go over the principle of operation and theory of how a jet pump works.

 

[Vumad]

Prop pitch is like tire size. Put a smaller tire on your car and it will accelerate faster, but loose top speed. Put a larger diameter tire on your car and you will loose acceleration but gain top speed.

--Prop pitch is kind of like tire diameter, except the diameter doesn't change, rather the angle of the blade changes.
--Lower number blades allow the motor to rev faster, hitting the powerband sooner, giving you most of your useable power at a lower speed, you accelerate harder, but you wont go as fast (small tire).
--Higher pitch blades put more drag on the motor, so the motor revs slower, but they move more what, so the useable power of the motor is much longer, giving you more top speed (bigger tires).
--Prop pitch with 2 numbers (IE 10/18) is a variable pitch, meaning the leading edge of the prop is a 10 and the tail edge is an 18. This gives a more progressive movement of the water and is more efficient. So, say before you can run a 16 pitch prop, with a variable pitch, you could go 10/18. The prop load is progressive, so now you can run a higher pitch prop of 18, because it starts out as a 10, improving its efficiency moving the water.

Other parts of the prop are the leading edge and the hub.
The leading edge of straight blade props hits the water bluntly and makes turbulence.
Swirl bladed props spread the hit out, making the movement smoother and more consistent.
Larger hubs increase pump pressures and reduce cavitation. You need the right pump setup to use such a prop.
Pumper stuffers (go where the intake grate is) increase inlet track speed

Mag pumps have less flex. The stator sections are more aggressive and there are usually more stator veins. The water comes out of the pump in a swirl motion. Mag pumps force it to go out more straight.

Reduction nozzles and tail cones...
Your pump moves water. It can move waters by two measurements. Volume or pressure. Think of your water hose. You turn it on half way and you get a certain volume of water at a certain pressure. Open the valve all the way and you get more water and more pressure. However, you are now maxed out. You now have a choice. Add a bigger hose to move more volume but loose the pressure, or add a nozzle which increases the pressure but lowers the volume.

Adding a pipe to a stock ski is like opening the valve on your waterhose. However, once you have opened that valve all the way (no more power upgrades), you have to tune the pump. Producing more volume will make you accelerate faster (freeride) and producing more pressure will make you go faster (racing).
Boring the reduction nozzle or stubby tail cones decreases pressure but increases volume, less motor load, more water over a larger area, you accelerate faster.
Going to a larger pump does the same thing, except it spreads the water over a larger area, so when you pump pushes water out, you have more water behind you pushing back.

Scoop intakes move more water to the top of the pump so you cavitate less, but scrub top speed and pull the ski down to the water.

Cavitating is air in your pump.

Guys, Feel free to quote me and correct any errors.

 

[hugh jair]

wow excellent breakdown guys i truly appreciate it and now understand WAYYY more about the thrust system in my boat thank you so much.
so to recap the xx/yy numbers on an impeller are different start/end poins of a "mixed pitch" prop not unlike the "twist" that exist im my heli's blades, makes so much sense now.

as well the importance of the wear ring to prevent what one could call blow-through i suppose, ie water being forced past the impeller without being part of the pump system benefits..in essence taking away some of its benefits, i have once sucked up a small stick and she'd rev and vibrate and not move, then i saw this twig wedged between the blade and ring..worse case scenario of course but same principle of tolerance too large and loss of thust.

the garden hose analogy is perfect and makes me grasp cones/reduction nozzles at last..and now i can clearly see how you almost need a doctorate to fine tune every piece of the puzzle lol

finding the right mix of impeller/nozzle/cone is still complicated but at least i now grasp the basics of it.

with all things being equal would'nt the previously mentioned "adjustable" cone be the best thing?? giving you the most bottom end hit and then adjusting itself to give you the best top end as well.

i finally understand the biggest difference between a freestyle boat and a race boat lies in the pump..ie i can change all i want in my octane engine bay but she'll generally handle the same, changing cones would give me more bottom end hit..combine cone with impeller..even more...or whichever hundreds..if not thousands of variations thereof..
this also strat to make me understand the differences in pumps ie 140 144 etc.

again thank you both for the informative breakdown

 

[Vumad]

with all things being equal would'nt the previously mentioned "adjustable" cone be the best thing?? giving you the most bottom end hit and then adjusting itself to give you the best top end as well.

Not necessarily. Think of an adjustable handle pole. You get the adjustment by either making it weaker, or making it heavier. Everything has a trade off, and a variable tail cone will outperform neither a stock nor a stubby tail cone. It may be the most versatile, but if you are setting your ski up for something specific, it is not the best.

i finally understand the biggest difference between a freestyle boat and a race boat lies in the pump..ie i can change all i want in my octane engine bay but she'll generally handle the same, changing cones would give me more bottom end hit..combine cone with impeller..even more...or whichever hundreds..if not thousands of variations thereof..
this also strat to make me understand the differences in pumps ie 140 144 etc.

This is not true. You can't take a freeride boat and put a different pump in it and call it a race boat. The biggest difference is in the overall package, not individual components. yes, a race boat may have a smaller nozzle, longer tail cone and steeper prop, but that isn't the whole of it. A race boat will also likely have larger carbs, more reserved timing on the top, higher port timing, perhaps a heavier flywheel, longer hull, perhaps with hull extension, maybe rear sponsons, probably weight in the nose or under the engine, and so forth.

Tuning a ski is like translating a language. If you translate word for word (component for component), the message will be lost. You have the translate the meaning (the package) to get the same result on the other end.

It's not just the pump that makes a race a race boat. It's how that engine, driveline and hull all work for the rider to reach the goal.

The reason the pump is such a big discussion for freeride and racing is because commong bolt ons increase power everywhere, so people tune the pump. Think of a SXR with a wetpipe vs a dry pipe. The wet pipe is lighter and makes good power, good for free ride and versatile riding, however, the dry pipe makes a lot more horsepower, turns a higher RPM and is the best for racing. yes, you can tune the pump, but the engine is an important part of the overall package. This becomes much mroe obvious when you get past basic bolt ons like ignition enhancers and a pipe.

 

[hugh jair]

ok granted i was evidently simplifying things a tad much.. i took it from the context of say an outboard motor, by changing nothing at all in the motor but trying different props you can get tons of bottom end torque and pull 4 guys out of the water behind the boat, same being said with a high speed prop where you couldnt get one guy out of the water but once on plane she'd get way more top speed....again, simplifying greatly.

i fully grasp the concept in regards to "the whole package" and realize there is much more at work between a race vs frestyle boat. that being said as per the op...its the driveline part of the package i was completely lost with and now thanks to you both i finally understand how said pieces of the puzzle start to fit together. ie you can tune an engine all you want, but you cant forget to tune the pump to that engine config..correct?? for example having the wrong parts in the driveline you could have a fantastic engine that doesnt rev out..or the opposite an engine that bangs off the rev limiter and the ski "feels" gutless ie over/under pitched... so, ultimately if you build/tune an engine to have monster bottom end and hit...your pump shold be set up to accoodate that, same with it you build an engine to scream at high rpm with gobs of pull on the top end, you want a pump set up that will let you squeeze all of that top end out.

or am i still comletely lost lol

 

[jetpilot808]

Those are great write ups, thanks guys!

 

[Vumad]

ok granted i was evidently simplifying things a tad much.. i took it from the context of say an outboard motor, by changing nothing at all in the motor but trying different props you can get tons of bottom end torque and pull 4 guys out of the water behind the boat, same being said with a high speed prop where you couldnt get one guy out of the water but once on plane she'd get way more top speed....again, simplifying greatly.

i fully grasp the concept in regards to "the whole package" and realize there is much more at work between a race vs frestyle boat. that being said as per the op...its the driveline part of the package i was completely lost with and now thanks to you both i finally understand how said pieces of the puzzle start to fit together. ie you can tune an engine all you want, but you cant forget to tune the pump to that engine config..correct?? for example having the wrong parts in the driveline you could have a fantastic engine that doesnt rev out..or the opposite an engine that bangs off the rev limiter and the ski "feels" gutless ie over/under pitched... so, ultimately if you build/tune an engine to have monster bottom end and hit...your pump shold be set up to accoodate that, same with it you build an engine to scream at high rpm with gobs of pull on the top end, you want a pump set up that will let you squeeze all of that top end out.

or am i still comletely lost lol

That's correct. You need a pump that matches the motor to get the most performance.

Also, you can make up for a motor that performs in the wrong area (Say you have a kawi ski and kawi motor but want more on the bottom and can't do anything about the high port timing nor afford a new motor) you only have the option of tuning the pump to try to make that power work where you want it. If money were no object, we'd all have 2 skis perfectly tuned for one thing. In reality though, sometimes we just have to tune the pump to stretch the buck.

 

[uwswimmer]

x2 on these being great write ups!

 

[NVJAY775]

Awesome topic and write ups. I think there are a few guys (builders) that are getting good at tuning pumps.

But to me it seems to be a fast evolving area in our freestyle world. There's a good handful of guys running LARGE pumps now. Stock being 144, and some are running 144, 148, 150, 155 and maybe bigger ones that I haven't heard of yet.

But getting them tuned to the engine is fun. I do dig playing with setups and learning this stuff though. In my experience and from just a gut feeling, I think propping down is going to be happening more. Especially under 900cc's. I'm at 5,000' and opened up my reduction nozzle a bit (144 mag) and went down to a 9/15 from a 10/16 and couldn't be happier in the bottom end hit department.

But from what I hear, some of the bigger engines are spinning / cavitating the smaller props and are having to go up. Although I can't quite get my head around that one yet. I get most of it, but not all of it lol.

Party on dudes!

 

[Vumad]

Awesome topic and write ups. I think there are a few guys (builders) that are getting good at tuning pumps.

But to me it seems to be a fast evolving area in our freestyle world. There's a good handful of guys running LARGE pumps now. Stock being 144, and some are running 144, 148, 150, 155 and maybe bigger ones that I haven't heard of yet.

But getting them tuned to the engine is fun. I do dig playing with setups and learning this stuff though. In my experience and from just a gut feeling, I think propping down is going to be happening more. Especially under 900cc's. I'm at 5,000' and opened up my reduction nozzle a bit (144 mag) and went down to a 9/15 from a 10/16 and couldn't be happier in the bottom end hit department.

But from what I hear, some of the bigger engines are spinning / cavitating the smaller props and are having to go up. Although I can't quite get my head around that one yet. I get most of it, but not all of it lol.

Party on dudes!

Going to bigger pumps is kind of like boring the nozzle. It lowers pressure and increases volume. More on the bottom. It spreads the foot print of the pump out over a larger area, so you have more water area pushing back at your pump. Gain on the bottom, lose on the top. Not right for everyone and every setup, but Options options. I might throw a stock 155 pump in my SJ someday, but probably not, because I hate trading my throttle for a wrench.

My tuning moto. If it wont blow up, lets go ride, we can dial it in later. :cheers:

 

[NVJAY775]

I'm looking forward to larger reduction nozzles / exit ring set ups for the 144 pumps.

I'm curious how far a 144 can be taken as far as engine cc size to pump ratio goes for flatwater / freeride hit? I (for some reason) think that if there were a larger ID reduction nozzle / steering nozzle set up, more hit could be achieved with a few less bucks. But the R n D has to be paid for fairly and I get that.

I've been trying to squeeze all the bottom hit I can out of my smaller engine.
5,000' elevation
781cc ported by I don't know who.
195 psi. comp.
62t cases, 61x cyl with 64x sleeves.
Flame TL
PFP
148 full specs not dialed yet
Boyesen intake system
144 mag non set back, 9/15 hooker
BG3 carbon hull.

I'm actually pretty stoked with my hit now, but I still want more! It's WAY more than it was a year ago with b pipe, same prop, msd enhancer and lower compression. HUGE differences. But I'm curious how much hit is available from a 144 with a larger reduction nozzle, then maybe propping it up a little if possible? How many cc's will it support?

I think there may be some available performance in there somewhere. A tad less weight and maybe save a buck in the process?

I'm sorry to the OP for the slight derail, but I think he may also understand where I'm coming from. Thought about starting a new thread on the subject... But this really is a good thread as is!

 

[hugh jair]

no worries at all, actually im glad it turned into such an informative discussion seeing as i feared being flamed with "use the search button", so as the discussion continues..it evolves..such is life and i can gain more knowledge from the different ideas being talked about, so have at it, thread jack away as long as its in regards to pumps, cones, impellers and how they all work together then ultimately..its relevant to the OP ;-)

 

[Little Trumps Super Jet]

very good read thanks!!! i understand alot more now