JT_Freeride
John Tetenes @Jtetenes
- Location
- Long Island
Can someone explain to me what exactly the benefits to a mag pump over stock are?
OEM 155 Pump Talk
- Thread starter DAG
- Start date
DAG
Yes, my balls tickled from that landing
- Location
- Charlotte, NC
know one is saying there is a magical setup? Go reread the post your are critiquing. For the guys that ride the white stuff there are things they can do to help. Yes of course, no mater how you tune a pump you are trading something to get something. Pumps don't make power so 100% every time you change something you loose a rpm to gain a rpm somewhere else. That's how fixed gears work
if all you know about pumps is what goes in the front comes out the back you aren't contributing anything to this thread, in fact you are doing quite the opposite. I've had my share of fluid dynamics but I by no means am a expert but let's try to contribute knowledge and theory to get a better understanding of how and why things work the way they do
- Location
- Long Island
speedysprocket
Alex
- Location
- Chesapeake, VA
Fluid dynamics was one of my favorite classes in school, and I wish I knew enough to apply math to this problem, but best I can say is this:
Water is not compressible. Air can be compressed.
Two 144 pumps take in say 50% water, 50% air.
Both pumps have an intake area of approximately 162 square cm (driveshaft area neglected).
Mag pump hub occupies 41 sq cm. So not taking into account the cross sectional area occupied by the vanes, there's a 25% reduction in cross section.
Now what's the diameter of a stock pump hub, like 60mm? I don't have one in at the office to measure...
Assuming that, cross sectional area is 28 sq cm. That results in a cross sectional area reduction of only 17%.
So, while it's still not ideal, the mag should compress 8% more air than the stock, resulting in 8% more water coming out as thrust.
Does that make sense? @DAG ...?
Water is not compressible. Air can be compressed.
Two 144 pumps take in say 50% water, 50% air.
Both pumps have an intake area of approximately 162 square cm (driveshaft area neglected).
Mag pump hub occupies 41 sq cm. So not taking into account the cross sectional area occupied by the vanes, there's a 25% reduction in cross section.
Now what's the diameter of a stock pump hub, like 60mm? I don't have one in at the office to measure...
Assuming that, cross sectional area is 28 sq cm. That results in a cross sectional area reduction of only 17%.
So, while it's still not ideal, the mag should compress 8% more air than the stock, resulting in 8% more water coming out as thrust.
Does that make sense? @DAG ...?
- Location
- Amherst NH
I gave my .02 earlier in this thread
The mag pump was designed in the hayday of racing . I would say with the introduction of the larger hub they were looking for more preasure and efficiency at high rpm's. How that rolls over into freeride/freestyle ...? I have been under the impression that more volume = more thrust. I know its not as exacting as that but it is a fact. Lets hear it from the fluid dynamic majors.
speedysprocket
Alex
- Location
- Chesapeake, VA
You know, decreasing that volume obviously increases the velocity, right? But counter intuitive to that is that as velocity increases, pressure actually decreases...
- Location
- Amherst NH
I dont get I
Correct so all things being equal meaning thrust speed out of the nozzle , more volume creates better thrust
- Location
- Amherst NH
My puny brain doesnt get It
speedysprocket
Alex
- Location
- Chesapeake, VA
No, I would say that is not correct. Thrust is the end result, but there's more than volume that goes into that.
air blair
you are the reason
- Location
- thumb, mich again
No as far as props in the 155. Oem b2 is 11/16 pitch. Great results dropping pitch numbers to 7/12 or 6/12 swirl thin blades. Sucks in water and allows prop to spin out faster. White wash aside. All around hookup is the goal. Top end I could careless about on freeride to freestyle, white water foam not even close to being a problem. I as steering away from scoop intake grates cause it scoops up too many rocks. A sacrifice of less hookup in chop. Won't effect white water or anything else I don't believe. Pitching down. To say a 6/11 to chase a 701cc engine is also a target I'm after.
Air blair cell
Air blair cell
D-Roc
I forgot!
- Location
- Dirty River Rider
Pumps are just like the other two parts of the ski (hull Engine)
If we apply the same principle to the pumps, we can make them perform to the best they can on any given setup. Engines have adj pipes, carbs, timing, exhaust valves, reeds. all to make the engine run to its best. hulls now have adj footholds, handpole length , ride plates and intakes all to help make the hull perform as well as possible with the riders size and weight. If you make your pump adj by different tail cones and reduction ring sizes I am confident you will make most prop pitchs perform well with your engine and hull. of course within reason. I have always gone with bigger is better. And if your running any taller of pitch than 13/17 for freestyle, you need a bigger pump.
Sent from my iSpud using Tapatalk
If we apply the same principle to the pumps, we can make them perform to the best they can on any given setup. Engines have adj pipes, carbs, timing, exhaust valves, reeds. all to make the engine run to its best. hulls now have adj footholds, handpole length , ride plates and intakes all to help make the hull perform as well as possible with the riders size and weight. If you make your pump adj by different tail cones and reduction ring sizes I am confident you will make most prop pitchs perform well with your engine and hull. of course within reason. I have always gone with bigger is better. And if your running any taller of pitch than 13/17 for freestyle, you need a bigger pump.
Sent from my iSpud using Tapatalk
air blair
you are the reason
- Location
- thumb, mich again
- Location
- Amherst NH
Maybe we are thinking of different terminology but what Im saying is if you have two identical hulls that displace water exactly alike , one hull has a pump nozzle that has a 12 inch opening that water is exiting and the other hull has a 3 inch nozzle , both nozzles have water exiting at 50 mph. The larger nozzle with more volume will reach top speed faster and would be able to maintain that top speed better and would be able to push a heavier weight to the same top speed as the smaller nozzle. Now Im just talking about a constant 50 mph out of the nozzle. Im not talking about any internal details of the pump. More volume equals more thrust.
That being said you cant just stick a massive nozzle on any pump and think your going to be getting the most thrust. But wouldn't a bigger hub setup create less volume that can be pushed from the pump? Isnt the bigger hub more suited for a higher preasure for better top speed on a boat that's up on plane?
All that being said I was able to ride the number 1 mod blaster a bunch of years ago and I think it had a 144 or smaller pump , not sure of mod rules but that boat hit off the bottom harder than anything Ive ridden.
- Location
- Savannah, GA
The way I understand it, when water enters the pump it is moving straight, but leaves the back of the impeller spinning with lots of turbulence. This is where the veins step in. As the water leaves the impeller spinning, it hits the veins which attempt to stop the spinning and guide the water straight out the back.
The water leaving the spinning impeller is really turbulent, turbulence equals water mixed with air, air compresses water does not, which means less thrust and less efficiency.
If the veins are spaced far apart, it allows more of this turbulence to get through. If you space the veins close together, there is more straightening of the spinning water and less turbulence getting though, which is more thrust. Apparently, this is also the effect it has on white water.
The faster the impeller spins, centrifugal force has a tendency to force the water to the outer edge of the impeller blades and pump, allowing turbulence to form near the center hub. By making the hub bigger it helps eliminate this turbulence because there is less room for low pressure flow.
Now whether these tricks that make a 144 mag pump more efficient, can cause it to outperform the extra volume of a stock 155, you will have to ask the guys that have tried it. Also, crappy pump tuned right can outperform a good pump set up wrong!
My 2 cents….
The tip speed of the impeller determines the max pressure. Bernoulli the reason we can and should use the largest hub possible. It is common to see 70MPH out of the nozzle. Now, understand that the tip speed of a 144 impeller spinning 7000rpm is 118MPH while the 75mm hub is only going 62MPH, a 50mm hub is only moving 42MPH. The slower moving water is at a higher pressure than the faster water that is further away from the hub. This water and whatever air present has to circulate into the faster moving fluid where the speed is averaged. The larger hub simply reduces the amount of dead water present. Entrained air will flow backward at the hub and short circuit the impeller until it clears. This is why large hub impellers work better.
DAG
Yes, my balls tickled from that landing
- Location
- Charlotte, NC
Good info on speed @kevbo thanks!
One question: I understand what you are saying speed relative to inside to outside edge but this sounds alittle like theory based on a flat rake across the prop. If we took into account Speed* Distance/Time Don't the props compensate for the lack of speed at the center with a larger angle? Aka why large hub props like a hooker have a consistent 6 degree pitch difference regardless of the pitch itself
One question: I understand what you are saying speed relative to inside to outside edge but this sounds alittle like theory based on a flat rake across the prop. If we took into account Speed* Distance/Time Don't the props compensate for the lack of speed at the center with a larger angle? Aka why large hub props like a hooker have a consistent 6 degree pitch difference regardless of the pitch itself
The inflowing stream is moving 1/3 as fast as the exit stream. The impeller root angle has to be steep enough not to impede inflowing water. This area is turning too slow to add any thrust, instead it serves only to push water away from the center. Modern ogive hub shape gets the maximum amount of water under blade then directs it outboard as it accelerates. Old small hub impellers allowed a lot of back flow at the root. This is why they make less thrust at low hull speeds (low head pressure) and in aerated water.
air blair
you are the reason
- Location
- thumb, mich again
Air blair cell
JT_Freeride
John Tetenes @Jtetenes
- Location
- Long Island
My big hub 7/12 works great but could use a little more snap off the bottom. I'll be in wavedaze I'll look for you and maybe we can get a side by side comparison.report back from a ride with an oem 760 prop. Yes it works but not so good. The big hub 6/12 I'm throwing in now the hub is significantly bigger. So great results will be felt first test will be in Virginia on this pump setup.
Air blair cell
speedysprocket
Alex
- Location
- Chesapeake, VA
Thanks for the added principles. It's been 7 years since I had a lesson in fluids, unfortunately. Can you talk to the vane number and shape...?