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Discussion Starter #1 (Edited)
This chart is my actual configuration (Q-Jet 750 and optimized timing). It is the most accurate data I have. "356 HP at 4700 RPM"
46469224_1870927909629639_1970992644259577856_n.jpg

This graph is an earlier dyno run and not as accurate as the chart. I am including it to show the wide band at which peak HP occurs:
45893101952_7565a2946a_o.jpg

Here is the Berkeley chart with the actual configuration data plotted "356 HP at 4700 RPM"
36851158543_f4b3191a72_o.jpg

Here is the Berkeley discussion on an archived page:

https://web.archive.org/web/20040220140713/https://www.berkeleyjet.com/Manuals/impeller.htm

I believe I need the AA impeller, since my HP/RPM plot is above the "A" line.
 

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Be careful as far as which company you buy your impeller from vs those charts; They all have slightly different power curves. I went with a Legend A impeller which was slightly tighter than the Berkeley A.

Also, the Legend Impeller had blades that are at a steeper angle; Theory- Your top end HP absorption is (Basically) set by the angle, while the LENGTH of the blades and their overlap sets your mid-range RPM......The idea here was to have longer blades at the steeper angle that still allowed the top RPM, while making the impeller more efficient at mid-range cruise. Basically, my 460/400HP still turns approx' 4800 rpm topped out, but the 30 mph cruise is now at 3000 rpm, rather than 3200 with the Berk A impeller. Kind of like an overdrive during cruise but with the same top end.

Legend was bought up by American Turbine, and I believe their "High-Helix" impeller is basically the same idea. You can supposedly still buy Legend parts from them.

And you can probably call them and ask about the right impeller size- having the exact HP curve on a dyno sheet makes it pretty accurate, so they can nail the proper size...

(I have a CVX-20 Jet w/460....I had the engine rebuilt along GM LS engine standards (Tight quench, wide lobe separation on the cam) and then installed a Edelbrock Carb with it leaned out in the midrange...(You can't load a jet heavy at low RPM- it just moves up in RPM).....Bottom line; I get better MPG than the DD ski boats.....And my boat is faster, quicker (And of course, more fun!!!)
 

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It'll struggle to pull a A to peak
 

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Discussion Starter #5
According to Berkeley "A" will never fully load the engine, unless I am reading it wrong. My Plot is above the A line.
 

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Buy the AA. If you try it and would like to have 400+- rpms more, then get it cut to an A. You can always cut smaller-- cant put it back on! :no:
 

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The scenario doesn't matter if only considering HP and impeller size. The larger unknown variable is: Is the boat and pump loading water?

It's safer to go larger with the impeller and have the option to cut it smaller.

To even consider an A impeller for a pump that is properly loaded at that HP is not even close.

If you buy a AA and start getting the pump to load you will more than likely end up cutting it many times.

Been there done that. I started with an A at 700 HP and when I worked on properly loading the pump ended up with a B/C

When I got the educated feedback I didn't argue I followed the advice. I closed off the full race intake opening with a custom shoe and started all over again.

Measure the pump intake pressures before making any decisions regarding impeller cut. If the pump is not properly loading water, Every effort is a waste of time.
 

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OP, what engine is this that only makes-"356 HP at 4700 RPM" and how hard do you want to turn it? 4700? What is the intended use?
 

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Problem is-- his engine is done before it gets on that chart.
Sure it's an example. No where near A or AA range was the point.
 

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Sure it's an example. No where near A or AA range was the point.
That all depends on how many rpm he is wanting from it. If you look at his chart above-- it is basically same as yours, just shows what he needs to see for his HP-RPM
Both of the charts are the same at 5200rpms, his just reads lower down the rpm range.
 

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Discussion Starter #13
Guys look at the Berkeley chart with the red cross hairs. That's where my engine plots. It's a SBC 406 somewhat set up as a torque engine. It has a Offenhauser Dual Port intake manifold. Family jet, maybe skiing, no racing. I specifically wanted a lower RPM engine.
 

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Guys look at the Berkeley chart with the red cross hairs. That's where my engine plots. It's a SBC 406 somewhat set up as a torque engine. It has a Offenhauser Dual Port intake manifold. Family jet, maybe skiing, no racing. I specifically wanted a lower RPM engine.
While your peak HP is above the line, does your HP stay above the A line curve the whole way up to peak? Once HP dips below the curve, it becomes very unlikely that you'll have enough slip in the pump to get the engine to accelerate and get to it's sweet spot on top of the curve. You could wind up stuck at a lower RPM and never make peak power. For example: if it takes 100 HP to move an object and you only have 98 HP, you'll never get it to move; even if it only takes 75 HP to keep it moving once it starts to move. Then look at the AA line and make the same comparison. Once you drop below the curve, how are you going to get back on top? Where you drop below is most likely very close to where you will stop accelerating.
 

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Guys look at the Berkeley chart with the red cross hairs. That's where my engine plots. It's a SBC 406 somewhat set up as a torque engine. It has a Offenhauser Dual Port intake manifold. Family jet, maybe skiing, no racing. I specifically wanted a lower RPM engine.
You should turn that AA almost 4600 with your power, the A would turn 4800--- pick your poison
 

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Discussion Starter #17
While your peak HP is above the line, does your HP stay above the A line curve the whole way up to peak? Once HP dips below the curve, it becomes very unlikely that you'll have enough slip in the pump to get the engine to accelerate and get to it's sweet spot on top of the curve. You could wind up stuck at a lower RPM and never make peak power. For example: if it takes 100 HP to move an object and you only have 98 HP, you'll never get it to move; even if it only takes 75 HP to keep it moving once it starts to move. Then look at the AA line and make the same comparison. Once you drop below the curve, how are you going to get back on top? Where you drop below is most likely very close to where you will stop accelerating.
Peak HP has been plotted at the RPM it occurs.
 

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parts and my location

Peak HP has been plotted at the RPM it occurs.
It's not just about where the peak HP is. You have to stay above the curve. But, Haas did the work for you. You'll loose a couple hundred RPM and not make it to peak HP using the AA. Which works best for you is up to you. Will you loose top end with the bigger/smaller impeller and a couple hundred less/more RPM? Will you launch quicker with the smaller/larger impeller? Pick your poison. As also mentioned earlier, you can always have the AA trimmed down. It wouldn't need to be trimmed all the way to an A to get you back the last couple hundred RPM. You might also consider what happens to your engine as it wears. Will it make more or less HP? If the impeller chart is spot on accurate (which they aren't), as soon as you drop below the HP curve (RPM & HP) your engine will stop accelerating and not make it to your peak HP. You are well above the curve until you get close to your peak HP with the AA. The A stays well above the curve. How comfortable are you that your HP will stay there or above?
 

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Discussion Starter #19
scon653 plot every rpm/hp plot in the dyno printout (the sheet with the numbers) on the Berkeley chart by hand and tell me what you see. I need an AA all the way up to the point I have plotted (max HP). Actually sometimes I even need an AAA. At those points (lower RPMs) the AA impeller is not fully loading the engine at any given RPM. Single A is never enough to load my engine through the entire power curve (up to max HP). If I am doing it wrong please show me with an example of your findings. I thought i was following Berkeley's instructions but perhaps I am not. Thanks.
 

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scon653 plot every rpm/hp plot in the dyno printout (the sheet with the numbers) on the Berkeley chart by hand and tell me what you see. I need an AA all the way up to the point I have plotted (max HP). Actually sometimes I even need an AAA. At those points (lower RPMs) the AA impeller is not fully loading the engine at any given RPM. Single A is never enough to load my engine through the entire power curve (up to max HP). If I am doing it wrong please show me with an example of your findings. I thought i was following Berkeley's instructions but perhaps I am not. Thanks.
John, Plot your HP at 4400, 4500, 4600, 4700, and 4800. Connect the dots and see where it crosses the AA line. Where it crosses is where the engine will stop accelerating due to not having enough HP to spin the impeller. Your peak HP plot is below the AA line, which means you won't get to it with an AA impeller. You never get close to the A impeller line. So "IF" you wanted to reach your max RPM and peak HP, you would need to use the A. Haas pointed out the same thing and even listed the RPM difference for you. It's not just an opinion. The chart shows the facts, even if you don't want them to be facts. But the charts are not 100% accurate, so believe what you want and use whichever you want. It is your football (I mean boat) and you can do whatever you like with it.
 
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