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Thread: A horsepower question.

  1. #16
    Left Coast Rider
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    Quote Originally Posted by twheats1 View Post
    Actually the horsepower reading will vary in the different gears, due to the torque multiplication that occurs in the transmission.

    To be accurate on a chassis dyno, one needs to pick the gear ratio closest to 1:1.
    This is why I said in my original post "thrust...is something entirely different."

    The engine produces 90hp. It will not produce more, or less, horsepower in a different gear.

    To quote a highly respected member here, "I have no idea, how discussions like this get started and how they morph into something totally different."
    Last edited by BC1100S; 04-26-2012 at 04:50 PM. Reason: typo

  2. #17
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    Quote Originally Posted by EMSimon View Post
    I know the XL1200 has more torque than my K1.
    It does? Perhaps more accessible at a lower rpm but more?

    And Brewmeister...nice to finally meet the guy who's been suckering me into those faux drag races all these years. Ya bastid !

  3. #18
    Registered User rxcrider's Avatar
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    Quote Originally Posted by oldnslow View Post
    If a bike is rated at, lets say 90 hp at 6000 rpm, is it producing 90 hp in any gear as long as it is turning at 6000 rpm.? Please lets not get crazy with hp loss due to drive train frictions and such. Lets agree that the bike is rated at 90 hp at the rear wheel at the ground.
    As you run past 6000 RPM at WOT, you should come close. If you don't have the throttle held all the way open, no.

    Other factors that will change your actual output relative to the rated value include:
    fuel charecteristics
    fuel temperature
    air pressure
    air temperature
    oil temperature
    head temperature
    humidity

  4. #19
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    Quote Originally Posted by rxcrider View Post
    As you run past 6000 RPM at WOT, you should come close. If you don't have the throttle held all the way open, no.

    Other factors that will change your actual output relative to the rated value include:
    fuel charecteristics
    fuel temperature
    air pressure
    air temperature
    oil temperature
    head temperature
    humidity
    Question: Have you ever had your bike on a dyno??? How are you getting to the rpm that is supposed to give you max hp (here: 6,000 rpm) without the throttle fully open?????
    In case you didn't know: On a dyno, you are running your engine against a load.
    You will have a hard time getting your engine up there without the thottle wide open. And of course, your SPECIFIED horsepower is at SPECIFIED ambient conditions.
    That's why a lot of dyno runs provide adjustements for the ACTUAL ambient conditions.

  5. #20
    Registered User rxcrider's Avatar
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    Quote Originally Posted by EMSimon View Post
    Question: Have you ever had your bike on a dyno??? How are you getting to the rpm that is supposed to give you max hp (here: 6,000 rpm) without the throttle fully open?????
    In case you didn't know: On a dyno, you are running your engine against a load.
    You will have a hard time getting your engine up there without the thottle wide open. And of course, your SPECIFIED horsepower is at SPECIFIED ambient conditions.
    That's why a lot of dyno runs provide adjustements for the ACTUAL ambient conditions.
    No, I've never had my bike on a dyno. I'm not racing and I have yet to be a better rider than my bike is a motorcycle, so I don't see the need. I'd be better off to spend my money on training and suspension. Regardless, I spend enough time staring at small engine performace data. The point of my post was that the OP didn't specify anything about WOT.
    ________________
    Quote:
    Originally Posted by oldnslow
    If a bike is rated at, lets say 90 hp at 6000 rpm, is it producing 90 hp in any gear as long as it is turning at 6000 rpm.? Please lets not get crazy with hp loss due to drive train frictions and such. Lets agree that the bike is rated at 90 hp at the rear wheel at the ground.
    _________________

    As for achieving 6000 RPM on a dyno without being at WOT, that depends on what mode you are running the dyno in. If you are using the dyno to siumulate inertia, rolling losses and air drag, you can probably run all day long in first gear @ 6000 RPM without being near WOT and thus, without producing anything near the rated power. Now, if you are accelerating at WOT through the 6000 RPM point, you should see something close to the rated power at that RPM.

    To put it another way, dyno or not, you can't get any more power out of the engine than you allow it to produce (throttle) and apply load to it.

    Also, correcting for ambient conditions doesn't mean your bike made the adjusted numbers. It just tries to put the numbers into a frame of reference for comparison purposes. The uncorrected numbers more accurately reflect how the engine actually performed.

    So to add a bit to my original response, As you run past 6000 RPM at WOT, under load, you should come close to producing the rated power.

    Hopefully that clarifies my point.

  6. #21
    Registered User Rod Sheridan's Avatar
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    Quote Originally Posted by EMSimon View Post
    I have no idea, how discussions like this get started and how they morph into something totally different.

    This was the original question:



    And the answer is: Yes! As long as the engine revs at 6,000 rpm, it turns out the rated horsepower of 90HP. No matter what gear you are in, you would measure 90 hp ( times efficiency, of course) at the rear wheel. The torque is different in different gears, yes, but so is the speed of the rear wheel in different gears, means the horsepower is the same - again under the assumption that the losses would be the same in different gears.
    No it doesn't.

    The engine only produces enough power to match the load, plus drivetrain losses.

    If load is low (flat ground, full speed in low gear), the engine power output is low.

    If the load is high, (High speed vehicle, high load due to aerodynamic and frictional load) then engine power output is high.

    Regards, Rod.
    Work is the curse of the riding class

  7. #22
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    And the descent into madness continues....

    No need to prove you're the smartest guy on the internetz, boys!

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