"A" impeller VS "AA" impeller

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Luckie Stiff

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« on: November 12, 2007, 08:00:09 PM »
What is the difference between the two?
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« Reply #1 on: November 12, 2007, 08:07:41 PM »
The AA is larger, and pushes more water, thus less RPM.

Alot of heavier boats use AA, us lighter boats can get away with an A or smaller

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« Reply #2 on: November 13, 2007, 07:32:31 PM »
Arent "A" impellers usually for bigger HP like 800 or above?
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« Reply #3 on: November 13, 2007, 07:35:59 PM »
Arent "A" impellers usually for bigger HP like 800 or above?

It all depends on where the HP is in the RPM range.

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« Reply #4 on: December 18, 2007, 08:03:42 PM »
What is the difference between the two?

the difference is in the diameter of the impeller, measured at the exit blades. on a AA, you'll notice the exit blades extend past the outside of the impeller flange. ON an A, the blades extend just to that flange.

the larger the impeller, the more water rides on the blades and therefore the more engine power is absorbed by the impeller. this is why a larger impeller will turn less peak rpm in your jet boat than a smaller diameter impeller.


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« Reply #5 on: December 21, 2007, 04:00:15 PM »
oh boy. No offense Jim, but aren't you running a "B" cut in a 90MPH class?

Typically an AA cut is used by a higher horsepower class. The more water your impeller can handle, the more water comes out the nozzle... You just have to have the HP and flow through the bowl to be able to handle it... To the HIGH POWER extreme you get to the point where you outflow the bowl and pressure builds up. Causes the pump to in effect "burp" which sends a rush of water back through the suction and pops the back end of the boat out of the water. Causing more or less an "endo" effect.... Good shit. I would imagine it's pretty scary shit too. Only seen it once in a video. Heard about it a lot.

How much power you planning for?

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« Reply #6 on: December 22, 2007, 10:52:54 AM »
If this helps...

An AA impeller spinning at 5500RPM will move more water and generate more thrust then an A impeller spinning at 5500RPM.

However, due to the fact that an AA impeller moves more water at 5500RPM than an A at 5500RPM, it loads the engine more, which requires more hp to spin it at 5500RPM than an A requires to spin at 5500RPM.

According to the Berkeley Impeller Curve Chart, an AA impeller spinning at 4900RPM will move the same amount of water and generate the same amount of thrust as an A impeller spinning at 5200RPM. This is because an AA impeller at 4900RPM absorbs the same amount of horsepower as an A impeller spinning at 5200RPM. However, this is theoretical and assuming a perfect world, so there is a give and take depending on other factors within the pump.

If you swap from an A to an AA without making any changes to the engine, your 100% RPM value will drop...how much it drops depends on the hp curve of the engine.
« Last Edit: December 22, 2007, 11:13:14 AM by Jetaholic »
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« Reply #7 on: December 23, 2007, 09:21:56 AM »
If this helps...

An AA impeller spinning at 5500RPM will move more water and generate more thrust then an A impeller spinning at 5500RPM.

However, due to the fact that an AA impeller moves more water at 5500RPM than an A at 5500RPM, it loads the engine more, which requires more hp to spin it at 5500RPM than an A requires to spin at 5500RPM.

According to the Berkeley Impeller Curve Chart, an AA impeller spinning at 4900RPM will move the same amount of water and generate the same amount of thrust as an A impeller spinning at 5200RPM. This is because an AA impeller at 4900RPM absorbs the same amount of horsepower as an A impeller spinning at 5200RPM. However, this is theoretical and assuming a perfect world, so there is a give and take depending on other factors within the pump.

If you swap from an A to an AA without making any changes to the engine, your 100% RPM value will drop...how much it drops depends on the hp curve of the engine.

Pretty good answer right there Skip ,Tom

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« Reply #8 on: December 23, 2007, 08:00:04 PM »
Is a berk chart applicable for agressor and dominator pumps? I heard the were 1 different say a berk "aa" is like a dominator" a" or do I have that backward?

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« Reply #9 on: December 24, 2007, 11:33:56 AM »
Is a berk chart applicable for agressor and dominator pumps? I heard the were 1 different say a berk "aa" is like a dominator" a" or do I have that backward?

I believe it is the other way around.
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« Reply #10 on: December 24, 2007, 12:04:40 PM »
I like the big impellers, more thrust at a lower RPM. Lower RPM means better fuel milage and less wear on the engine.  The bigger boats run big impellers, say a 9.5" and a A3. The boats that had Olds engines installed tipically had AA or A2 impellers installed at the factory.
It seems the the AT/Dominator impellers absorb more power than the same cut from Berk. Dave Jones at Aggressor explained it quite well to me, but I can't remember the  whole conversation. Now you that a Berk A2 impeller you can compair it to a Aggressor A. Dave Jones is a very nice guy that you should call and talk with. He can explain alot of the history of jet drives to you. He is always willing to share info. 
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http://www.aggressorjets.com/contactus.html

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« Reply #11 on: December 30, 2007, 11:46:19 AM »
If you go from a Berk A to an aggressor A, you can expect to spin 400 less RPMs at WOT. Aggressor takes the name seriously... And they do cut their impellers a bit more aggressively.

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« Reply #12 on: December 30, 2007, 01:20:47 PM »
If you go from a Berk A to an aggressor A, you can expect to spin 400 less RPMs at WOT. Aggressor takes the name seriously... And they do cut their impellers a bit more aggressively.
RPM does not always mean MPH !!!

Now this can be adjusted and tuned to get desired RPM by thrust and side clearance. If a pump is "Tight" it usually does not mean it does not turn free it means it is very eficiant. Now say you have a pump with .250 thrust clearance (mid '70s Factory clearance) vs a pump with .018 thrust clearance (Tight ass race pump) it will turn 200 - 400rpm less as well. I have seen people loose mph when they have a pump rebuilt because they don't have the power to turn the rpm they were able too with the old woreout 1970s pump.
You can also tune and adjust to get desired RPM and power of the engine by machining the trailing edges of the large and small diamiter of the impeller. That is where the size or cut are desided. A 9.5" impeller by AT has the same basic cut to the blades on the leading edge as a "B" (6.75") impeller.

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« Reply #13 on: December 30, 2007, 02:02:16 PM »
RPM does not always mean MPH !!!

I believe I stated this in my article regarding jet pump operation. RPM and MPH have nothing to do with each other. One boat spinning 4500RPM will do 65 while another one spinning the same RPM may only do 50. It's all relative to the weight of the boat and how much thrust you generate at certain RPMs. It's all about thrust/weight ratio. If you tighten up the pump you can generate more thrust by moving more water. This may or may not place a higher load on the engine at RPM...by also increasing the HP output of the motor to spin the RPM you could spin before the pump was tightened up, you can generate more thrust than you did before at that RPM, which will increase your MPH. The same applies for going from a smaller to a bigger impeller.
« Last Edit: December 30, 2007, 02:05:55 PM by Jetaholic »
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« Reply #14 on: December 30, 2007, 02:09:45 PM »
Just answer your pms

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« Reply #15 on: December 30, 2007, 02:10:21 PM »
I believe I stated this in my article regarding jet pump operation. RPM and MPH have nothing to do with each other. One boat spinning 4500RPM will do 65 while another one spinning the same RPM may only do 50. It's all relative to the weight of the boat and how much thrust you generate at certain RPMs. It's all about thrust/weight ratio. If you tighten up the pump you can generate more thrust by moving more water. This may or may not place a higher load on the engine at RPM...by also increasing the HP output of the motor to spin the RPM you could spin before the pump was tightened up, you can generate more thrust than you did before at that RPM, which will increase your MPH. The same applies for going from a smaller to a bigger impeller.

Damn now I am confused  ::)

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« Reply #16 on: January 02, 2008, 12:23:19 PM »
emanon, I'm not sure where you saw a gain in MPH claim in my post?
Well if your impeller is "tight," your suction adequate, and your bowl able to handle the CFM. Why would you flock around with taking away your impellers ability to flow water by loosening up the tolerances and shaving down the impeller? Instead of taking away from your impeller, you should be trying your damnedest to get the rest of your pump to keep up.
Assuming the rest of your pump is up to the task, you will absolutely GAIN MPH with the decrease in RPM caused by the more aggressive impeller.

Maybe I missed something, but I could have sworn your alias claimed "...Performance Marine." After all, you're pump is still wearing a "B" cut ain't it? I noticed you made a reference to Dave at Aggressor, perhaps you should listen a little more closely to what it is he has to say. Your boat might just fare a little better.
« Last Edit: January 02, 2008, 12:44:37 PM by UNDONE »

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« Reply #17 on: January 02, 2008, 12:41:38 PM »
thats gunna leave a mark :'(

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« Reply #18 on: January 02, 2008, 12:48:29 PM »
emanon, I'm not sure where you saw a gain in MPH claim in my post?
Well if your impeller is "tight," your suction adequate, and your bowl able to handle the CFM. Why would you flock around with taking away your impellers ability to flow water by loosening up the tolerances and shaving down the impeller? Instead of taking away from your impeller, you should be trying your damnedest to get the rest of your pump to keep up.
Assuming the rest of your pump is up to the task, you will absolutely GAIN MPH with the decrease in RPM.

Maybe I missed something, but I could have sworn your alias claimed "...Performance Marine." After all, you're pump is still wearing a "B" cut ain't it? I noticed you made a reference to Dave at Aggressor, perhaps you should listen a little more closely to what it is he has to say. Your boat might just fare a little better.

It is called tuning, but hay my boat and any I set up work great and very consistant.
Is there a differance between a Berk "A" and a MPD "A", rpm and thrust wise ?
Do you think and old loose pump Boat is always slower or faster than with a new rebuilt tight pump boat ?
No I change the pump around quite often but the Berk pump has had a Heritage MPD "A" impeller, that is flowed on the front side, in it for quite some time. If I didn't listen to Dave I would still have an AT impeller in it.

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« Reply #19 on: January 02, 2008, 03:56:33 PM »
You and your sanger were mentioned the other day. I'll leave it at that.
« Last Edit: January 02, 2008, 04:04:02 PM by UNDONE »

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« Reply #20 on: January 02, 2008, 05:21:07 PM »
You and your sanger were mentioned the other day. I'll leave it at that.

Gosh that has never happend before. ::)
Let me think it is the worst handling boat to ever run the circles and should not even be racing.
As far as me being mentioned, let me think, mmmmmmmm I am a danger to all those around me and I am bringing the sport down.

Does that about cover it ?

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« Reply #21 on: January 02, 2008, 05:26:59 PM »
Hey Skip,
Are you even more confused than before ??? I sure am. I think I will leave my pump alone. ;D
the jet boat never did this to you bob ::)
Can I get next in line behind The Beav

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« Reply #22 on: January 03, 2008, 12:53:28 AM »
Hey Skip,
Are you even more confused than before ??? I sure am. I think I will leave my pump alone. ;D

To end the confusion once and for all and get the thread back on topic...

Quote from: Jetaholic
If this helps...

An AA impeller spinning at 5500RPM will move more water and generate more thrust then an A impeller spinning at 5500RPM.

However, due to the fact that an AA impeller moves more water at 5500RPM than an A at 5500RPM, it loads the engine more, which requires more hp to spin it at 5500RPM than an A requires to spin at 5500RPM.

According to the Berkeley Impeller Curve Chart, an AA impeller spinning at 4900RPM will move the same amount of water and generate the same amount of thrust as an A impeller spinning at 5200RPM. This is because an AA impeller at 4900RPM absorbs the same amount of horsepower as an A impeller spinning at 5200RPM. However, this is theoretical and assuming a perfect world, so there is a give and take depending on other factors within the pump.

If you swap from an A to an AA without making any changes to the engine, your 100% RPM value will drop...how much it drops depends on the hp curve of the engine.
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« Reply #23 on: January 05, 2008, 10:23:05 AM »
I like the big impellers, more thrust at a lower RPM. Lower RPM means better fuel milage and less wear on the engine. 

Less wear on the engine...yes. Lower RPM = better fuel mileage...not exactly.

Fuel consumption is governed by how much power is being made, not by how fast or slow the engine spins. Remember this law of energy?

"Energy can neither be created nor destroyed. It can only change form."

An engine converts combustion energy (the ignition and explosion of fuel and air within the cylinder) into reciprocating energy. It then converts the reciprocating energy (i.e. the pistons moving up and down) into rotary energy (the rotating motion of the crank).

It takes a certain amount of fuel to make a certain amount of horsepower. It doesn't matter if you're making that power at 3,000RPMs, 4,000RPMs, 5,000RPMs, etc etc. If the same amount of power is being made at 4,000RPMs as is being made at 5,000RPMs, the engine will require the same amount of fuel regardless of the RPM.

The engine has to make a certain amount of power to generate a certain amount of thrust. In regards to fuel consumtion, it doesn't matter at what RPM it makes it at. The engine will still consume the same amount of fuel to make that certain amount of power. Engine vaccuum controls how much fuel is consumed, and the load placed on the engine controls how much vaccuum you have. More load = less vaccuum = more air = more fuel. RPM has nothing to do with it.

As far as the "more thrust at lower RPM with a bigger impeller", actually you get the same thrust at lower RPM. And yes your RPM may be lower, but if you're making the same amount of thrust at a lower RPM, the pump is requiring the same amount of horsepower as it would at a higher RPM with a smaller impeller to move the same amount of water to create the same amount of thrust.

You can also switch to a bigger impeller to increase the speed of the boat. Let's say for instance with an A impeller your top RPM is 5500RPM. You then switch to an AA impeller. This will load the motor more and drop your 100% RPM value. However, by beefing up the motor so that you can spin the AA impeller to 5500RPM, you will gain MPH because the AA impeller will move more water at 5500RPM than the A impeller would, thus generating more thrust.
« Last Edit: January 05, 2008, 12:39:41 PM by Jetaholic »
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« Reply #24 on: January 05, 2008, 12:24:56 PM »
Your right I'm 100% wrong. I have quit building boats and custom jet pumps so I can go to work for UPS. I just got a offered a position loading trucks for them here at the Bullhead Depot.

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