Speeds fine. but don't always need. Questions?
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Speeds fine. but don't always need. Questions?

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    Default Speeds fine. but don't always need. Questions?

    I know nothing, compaired to you guys, but trying to wrap my head around all this info.A jet pump runs best/efficient about 8500 RPM? Right/Wrong? Also is a Motor most efficient at Torque Peak , H.P. peak or someplace else? If my motor does'nt make it to peak but goes to satisfication speeds is there more incentive efficiencly wise to increase RPM to peak? Whatever HP or Torque? Right now I run Great MPG annd great Performance (for me) just wondering on extending range mostly. My baja is a little squirrely at only 60. I don't care, it's fine and I like it. But trying to decide if maybe I should cut my impellor. Big/slow = Efficient, OR not? Would peak motor curve? help in petrol used or not.

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  3. #2
    "Need For Speed" Gearhead's Avatar
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    Quote Originally Posted by BAJA JA View Post
    I know nothing, compaired to you guys, but trying to wrap my head around all this info.A jet pump runs best/efficient about 8500 RPM? Right/Wrong? Also is a Motor most efficient at Torque Peak , H.P. peak or someplace else? If my motor does'nt make it to peak but goes to satisfication speeds is there more incentive efficiencly wise to increase RPM to peak? Whatever HP or Torque? Right now I run Great MPG annd great Performance (for me) just wondering on extending range mostly. My baja is a little squirrely at only 60. I don't care, it's fine and I like it. But trying to decide if maybe I should cut my impellor. Big/slow = Efficient, OR not? Would peak motor curve? help in petrol used or not.
    I'm probably not the best to reply to this question, but I'll get the discussion started. First, there is quite a bit of difference in how you approach this question as it directly relates to useage, engine style and power curve, hull design, etc. BP298 touched on this pretty well in the "gearbox" discussion recently.

    For most receational lake style jetboats, the majority of the boats out there, the engine power curves along with the pump efficiencies and hull efficiencies are going to be between 5000 and 6500 RPM and less than 100 MPH crafts. Using an engine and impeller to operate in this range, which generally will be something between a AA to a B size impeller will offer you the best performance and fuel economy.

    The RPM ranges, impeller sizes and gearbox useage that has been in discussion lately where the engines and/or pumps operate in excess of 8000 RPM is very limited and is being used in very specialized race style boats. These boats are not concerned with cruising around the lake, skiing or fuel economy.

    These race boats have jetpumps that have been highly modified to opearate with a highly modified and expensive racing engine that will be used in a light weight race hull that has hardware thatis very specialized and highly modified.

    In no way an I trying to talk down or belittle your thoughts. I see where some of the technical race talk can be confusing to the general jetboat enthusiast. I operate my lake boats very differently than my race boat.

    I hope this helps a little. The most common impeller in most lake jetboats is probably an "A" impeller operating between 4600 and 5400 RPM. This works best with the power curve of a generally available big block automotive engine. After that the world is your limit Above all, HAVE FUN within your budget!!! What is a budget???

    Gear
    Last edited by Gearhead; 01-29-2012 at 02:01 PM.

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