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"A" impeller VS "AA" impeller

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« Reply #25 on: January 10, 2008, 05:54:09 PM »
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.

That was an INCREDIBLY "LOGICAL" post..... You should put some more thought into what you just said.


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« Reply #26 on: January 11, 2008, 01:56:17 PM »
More RPM always = more demand for fuel. The more those valves are opening the more air and fuel they require... If you're making 500HP at 3000 RPMs would it not make sense that maintaining an equal amount of HP at 4000 RPMs would require more fuel? After all It does take power to get those extra RPMs turning. To further my point, I'll use my brand new truck as an example. It makes peak HP and torque right around 3200 RPMs... However, as the RPMs turn higher and the power starts to die off the fuel mileage continues to decline.

Also, in my 18' Caribbean with roughly 550HP running 5200 RPMs would go through 6 gallons of gas in one loop around Buena Vista in Bakersfield. Where as, running 4800 would use 4. The MPH difference was on average 7MPH between the two RPM ranges.
At 4800 it was doing either 64 or 67 I don't remember.
I believe there is A LOT you haven't considered.
More RPMs = more fuel = worse fuel mileage.

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« Reply #27 on: January 11, 2008, 03:26:08 PM »
I think you're misunderstanding what I'm saying.

Let's take your boat for example. At 5200 RPM you would go through 6 gallons of gas around the BV loop. Then when you drop the RPM to 4800 it only uses 4 going the same distance. All you did was change the throttle position to drop the RPM, which will in fact decrease fuel consumption. This is because with the same impeller the engine will see less of a load at the lower RPM.

However, let's say that with an A impeller your max RPM is 5200. Then you swap it to an AA impeller and your max RPM drops to 4800. And let's say that at 4800RPM the AA impeller places the same load on the engine as the A impeller spinning at 5200. Even though your max RPM dropped, your fuel consumption will be the same as with the A impeller spinning at 5200RPM. This is because the same exact load is being placed on the engine, which will require the same amount of fuel to make the same power it made at 5200RPM with the A impeller.
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« Reply #28 on: January 11, 2008, 03:44:18 PM »
I misunderstood. Now it's all making sense to me... Based solely on what your post was claiming, can you see how I could be confused?


"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."

Even so I'm not sure that is entirely untrue, the engine is still making the same amount of power (at a given RPM as it was before) so now your carb is just dumping excess fuel, right?

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« Reply #29 on: January 11, 2008, 04:06:15 PM »
I misunderstood. Now it's all making sense to me... Based solely on what your post was claiming, can you see how I could be confused?



I do see where you could be confused. The whole point of this post was because Jim Rich claimed that with a bigger impeller you could get the same thrust at a lower RPM and not use as much fuel, and I was merely trying to correct this.

To answer your question...fuel is an energy source. It takes X amount of energy to perform X amount of work. This basically means that an engine requires X amount of fuel to produce X amount of power. Remember, energy can neither be created or destroyed...it can only change form. In the case of an internal combustion engine, you convert combustion energy into reciprocating energy (the up and down movement of the pistons). You then convert reciprocating energy into rotary energy (the rotation of the crank). Having said that, there is no way that you can make the same amount of power with less fuel just because of RPM. You get what you put in.
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« Reply #30 on: January 15, 2008, 12:40:11 PM »
Being you are using therory instead of practical application you are just guessing and grasping at straws. Once you actually try one back to back in a test then and only then can you make any claims. You need to really do some real world tests John. How many pumps have you done by yourself, and what was the out come ? Stop trying to baffle these guys with all your BS. As I said last night Keep It Simple Stupid !

Now here is what you were asking  about last night.

AT built in stuffer and Blue wear ring

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« Reply #31 on: January 15, 2008, 01:57:34 PM »
AT's semi-sad attempt at a built in bowl stuffer... cutesie shit right there. They try too hard to buy out smaller companies and don't spend enough time actually researching...

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« Reply #32 on: January 15, 2008, 02:01:33 PM »
AT's semi-sad attempt at a built in bowl stuffer... cutesie shit right there. They try too hard to buy out smaller companies and don't spend enough time actually researching...

How is that semi sad? Looks like it would be pretty effective to me

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« Reply #33 on: January 15, 2008, 03:00:27 PM »
AT's semi-sad attempt at a built in bowl stuffer... cutesie shit right there. They try too hard to buy out smaller companies and don't spend enough time actually researching...

Well Dave and I talked a bit today, he is not back yet but is returning a few calls.

The AT deal is very effective but the impeller itself does not lend a very good helpful hand in thrust.  That must be the why they are working on the new Hihelix design impellers.  But Aggressor has a new design too and it should be even more efficient then their other impellers.  Dave stated today that their A impeller will spin 400 rpm less than a Berk A and create more thrust, higher speed.  I am pretty sure that being the Aggressor impeller is made in 4 parts which is a much better and aggresive design than the 1 step AT.  But the AT stuffer is still much better in my eyes.  But this season I will be running Aggressor impellers in my CJ boat exclusively.  Now the tin boat will run a 10" AT with lip, it is not a high speed boat so low rpm efficiency is most important and the AT 10" gives that.

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« Reply #34 on: January 15, 2008, 03:05:04 PM »
I've always like that feature myself, it dates back to the original Mar-Bud Dominators.  From a production standpoint its pretty smart, not much attention has to be paid to set it up correctly, rareley have I ever had a back space problem. And though it doesnt close down the void it does appear to seal it up fairly well.

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« Reply #35 on: January 15, 2008, 03:17:55 PM »
well put Josh. It is semi sad because they had a good idea and never fully developed it, they started then kinda let off. Dave's new impeller is worth the wait. You guys are gonna like it.

 


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