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Discussion Starter #1
After my race engine builder buddy freshened up my long rod 400 he put together for my old boat I put it in my new to me aluminum skiff, set the timing and proceeded to dial in the a/f ratio with my Guage. Last summer I decided to dial in the timing. After finding the sweet spot I find I'm turning my B impeller over 5800 rpm. It gets great mileage and will do over 60 with the primitive welded hull and cruises at 40 at 4000 rpm. Would I gain anything to run a bigger impeller or would I loose the fun factor? It accelerates hard and puts a grin on my face but over 60 my arm starts hurting from my wife hitting me while yelling slow down.

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Surely someone here has found themselves with more HP than they expected. A stainless impeller is too expensive to buy and try. I need some incouragement or discouragement from my fellow jet boaters.

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This is just my experience, I don't claim to be an expert.

If you are turning a B @ 5800, you are probably making about 500 HP or thereabouts. If you were to switch to an A, you would probably drop around 300-400 RPM @ WOT. Your cruise RPM will drop some too, but probably not as much. Your range may increase slightly doing so. An aluminum impeller will easily stand up to that power level as long as it isn't being abused. The A impeller would also probably improve your holeshot some.

This is assuming that you are running a Berkeley or Berkeley type pump.

You can find a pump curve chart if you google "Berkeley impeller chart".

Hope this helps.
 

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Thanks for your input. I have a dominator set up tight with ultimate wear ring. It accelerates hard now out of the hole now. I have an inducer and the boat weighs around 3000 Lbs. It's minimum planing speed seems to be 22-25 and that takes around 3200 rpm to achieve.

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If you change your impellor you need to make sure your horsepower curve stays above the impellors curve. If your power drops below the impellor curve you will stop accelerating and you are stuck at that rpm. The pump on your boat is like running against a dyno every time you push it. So you can try the A wheel, but it is best if you have at least an idea what your horsepower curve looks like and compare that to the horsepower required to spin the impellor. A jet boat isn't like a prop boat or a car where the prop or tires can spin and get you past the horsepower curve and then hook up and leave you at the higher rpm. If the RPM horsepower curve doesn't stay above the impellor horsepower curve you can't get to your max horsepower as it will simply stop building rpm.
 

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Discussion Starter #6
So you're saying I could loose the fun factor by loading it more. I thought you had to run bronze or stainless above 450-500hp. I could try an aluminum A and if it loads my motor to much cut it to an AB.

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