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Calculation of an engine power

  1. Mar 20, 2010 #1
    Actually i wanna find the required power of an a single cylinder air cooled 4 stroke OHV engine. i have calculated three power losses, power loss against road gradient (Pg), rolling resistance (Pr) and drag (Pd) using the following formulae:
    Pg=M*g*v*grad=1.095 hp
    M(mass of the prototype car)=120kg, g=9.8 m/s^2, v(prototype car velocity)=13.88 m/s, road gradient= 5% (0.05)
    Pr=RRC*M*g*v=0.109 hp
    RRC (rolling resistance coefficient)=0.005 for a bicycle tire we are using in our prototype car
    Pd=0.5*rho*v^3*Cd*A = 0.030 hp
    rho=1.099 kg/m^3, Cd (Coefficient of drag)=0.04 in case of our prototype car, A=0.384 m^2
    Net power losses=Pg+Pr+Pd=1.234 hp.
    Now please tell me can i use an engine of 1.3 hp of 35cc volumetric capacity in our prototype three wheeled car. Generator is the only accessory that will be connected with the engine to charge the battery.13.88 m/s will be the max. speed of our prototype car, 120 kg is the mass of the prototype with driver. reply soon please
  2. jcsd
  3. Mar 20, 2010 #2


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    Did you calculate the rolling resistance for all wheels?
    Have you applied a safety factor, and an allowance for acceleration (and not just travel at a constant speed)?
    Have you considered friction in your drivetrain?
    Have you considered conversion losses through the powertrain (including your 'generator'?)
    Is your engine going to be operating at optimum conditions for 1.3hp?
  4. Mar 21, 2010 #3
    ok.thnx.tell me plz the procedure of how to calculate the power losses of engine through transmission.
  5. Mar 28, 2010 #4

    jack action

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    For every gear set or belt drive set, assume 95% efficiency. For every chain drive set, assume 92% efficiency. Multiply all of them for overall efficiency.


    if the power of your engine goes through 3 gear sets before reaching the wheels, your overall efficiency would be 0.95*0.95*0.95 = 0.857. So if you need 1.234 hp at the wheel, you need 1.234 / 0.857 = 1.44 hp at the engine.
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