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Thread: Installing a higher pitch impeller?

  1. #1
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    Default Installing a higher pitch impeller?

    Looking for input/advice and whether or not this is even "doable". Considering getting a higher pitch impeller installed on my 02 Duckworth Advantage (302). I'm thinking this would give me a faster top end, and better fuel economy. the 302 has plenty of torque, but I have to keep it pretty wound up to stay on a good plane (open water).

  2. #2
    Member captaindd's Avatar
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    Default Prop

    The higher pitch prop will give you the higher top end but will be harder for you to get on plane and to maintain a plane in rough water. I did the same thing in one of my boats and while it performed better in flat water you increase your load or have to slow down because of water conditions you loses every thing that you gained. If you take your current boat setup and add all the extra gear and weight that you normally carry what is your maxium rpms under full load? If you can reach maxium RPM's under your current setup going up in pitch with not get you the performance you want. I am currently going up in pitch on my boat for the same reason that you are but when I purchased my boat it had higher pitch props on it than it does now. My boat with G-5 Props cruises at 3000 RPM =30Knots top speed 36.5Knots 3620 RPMs when I tested the boat with G-6 props 3000 RPM =33Knots top speed 39.5 Knots 3620 RPMs I have a friend who has a similar size boat who runs G-7 props his cruise is 30Kt at 2750 RPM top speed 42.5 K at 3620 RPM To change out my props has cost me $2100 and I am hoping to get an improved mileage from 1.4 mpg to 1.7 mpg that would save me about $3000 this summer.

  3. #3

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    You do not want to change the pitch of your impellers. Changing the pitch of the impellers will not result in changes in performance like changing the diameter and pitch of a propeller will.
    What pitch or "cut impeller you need to run is based on the Hp of thr engine and what RPM the max Hp is generated at, each manufacture has a chart for impeller selection.
    If you get an impeller that has to steep of a pitch the engine will tend to bog and you will not be able to get the engine up to max rpm and you wont be able to pick up as much weight, if you go with a pitch that is shorter then you will cavitate coming out of the hole and your top speed will be lower plus you could over rev the engine.
    A jet unit is basically a positive displacement pump and with a positive displacement pump it takes x amount of Hp to move y gal/min of flow, unless you change the entire pump housing (jet unit) the Hp/flow will not change.

  4. #4

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    After reading the last thread about changing pumps for better performance, i was wondering if there are better pumps for outboards? I think mine is fine, just want to see if maybe there is an option for upgrading to something better. I have an older one i guess, since its probably been with the motor since 1985. The foots been replaced though before i bought it, looked at it and it looked farely new (no sun fade). The boat does pretty good as far as performance im guessing. It does have a 2 stroke motor on it so i guess i shouldn't expect to much in fuel economy.

  5. #5

    Default impeller

    Quote Originally Posted by kdp View Post
    Looking for input/advice and whether or not this is even "doable". Considering getting a higher pitch impeller installed on my 02 Duckworth Advantage (302). I'm thinking this would give me a faster top end, and better fuel economy. the 302 has plenty of torque, but I have to keep it pretty wound up to stay on a good plane (open water).
    I'm guessing you have an American turbine jet "white", or Marine power Extreme jet "silver grey" which is just a copy of the AT single stage pump. Why not get a new impeller? How many rocks or gravel/sand has it had ran through it. just a new impeller may do the trick, they also offer a stainless one yours is probably an aluminum one. There are several sizes of impellers for them and a new inducer impeller which is supposed to help as well. I bet some one out there can give more info on these. Or call the guys at the pump manufacturer and they can give you the impeller that the 302 is best suited for.

  6. #6

    Default

    Here are some things to check that will help ensure that the pump achieves optimum performance. First thing is the impeller, the leading edges should be smooth and even if they are not use a file and clean them up do not sharpen them to a knife edge because the thin edge will curl during use and cause cavitation. Next ensure that the blades of the impeller are smooth and there are no dents all the way to the discharge of the impeller. Then do the same checks for the leading edges and the vanes of the volute/discharge vanes of the pump. the next thing to check (and the most overlooked) is the wear ring between the bowl and the impeller, the tolerance between the impeller and the wear ring is critical if the the gap get to big the pumps performance will suffer greatly because the high pressure water from the impeller discharge will leak through to the low pressure inlet side of the impeller, the gap should be checked with a feeler gauge unless you can eyeball a couple of thousandths of an inch. If your wear ring is over 3 years old there is a good chance that it will be out of tolerance.

  7. #7

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    Quote Originally Posted by 21'-Grayling View Post
    After reading the last thread about changing pumps for better performance, i was wondering if there are better pumps for outboards? I think mine is fine, just want to see if maybe there is an option for upgrading to something better. I have an older one i guess, since its probably been with the motor since 1985. The foots been replaced though before i bought it, looked at it and it looked farely new (no sun fade). The boat does pretty good as far as performance im guessing. It does have a 2 stroke motor on it so i guess i shouldn't expect to much in fuel economy.
    The problem with the red outboard jet units is that most of the energy the impeller transmitts to the water is used to push the water through the 400 degrees of turns between the impeller discharge and the jet exhaust.

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