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Newbie BHP vs WHP question

Discussion in 'General Automotive Discussion' started by Bowers, Dec 19, 2007.

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  1. Bowers

    Bowers Karting

    Sep 27, 2007
    242
    San Jose
    Full Name:
    Bowers
    #1 Bowers, Dec 19, 2007
    Hello all, I know this is a newbie question but I have been unable to find an answer. Why is BHP different from WHP? Where did the lost ponies go? What happens between the crank and the wheels that causes the lost power?

    I was always under the impression that torque is what turns the driveline, and wheels for that matter. I know, I know horsepower is not the important number because it is in fact calculated using the torque output over rotation per minute divided by feet in a meter yada, yada, yada I know what horsepower is and how it works, how it’s calculated.

    I am interested in why there’s a difference between BHP and WHP. Sometimes as much as 20%, where did it go?
     
  2. ascari_2

    ascari_2 Karting

    Oct 9, 2005
    154
    Chicago area
    Full Name:
    Yuri
    #2 ascari_2, Dec 19, 2007
    There are loses in the transmission due to friction. So the more places where there is friction, the more loss you have. By the time it gets to the wheels there is usually between 10 and 20% loss depending on the transmission.
     
  3. Bowers

    Bowers Karting

    Sep 27, 2007
    242
    San Jose
    Full Name:
    Bowers
    #3 Bowers, Dec 19, 2007
    I always thought the transmission, in its most basic form, harnessed the power of the engines 7500 rpms into a far more realistic rotation of witch you tires is doing, making torque.

    So the horsepower is lost in the transmission making torque? Then why is horsepower calculated from torque? It seems the equation is going the wrong way.
     
  4. James_Woods

    James_Woods F1 World Champ

    May 17, 2006
    12,755
    Dallas, Tx.
    Full Name:
    James K. Woods
    #4 James_Woods, Dec 19, 2007
    Let me try a shot at this one:

    a) you are right on the horsepower being lost in the transmission. The transmission does not "make torque". This may be what we are missing here...the engine "makes" the torque, but the RPM is too high for use at the wheels. So, the transmission & differential conspire to bring down the RPM to proper rate for the wheels, and do indeed increase the torque some in doing so. However, they cause a LOSS in total HP due to such factors as friction in the bearings & gears, losses in the case of a "torque convertor" (notice they do not call it "torque maker"), oil & grease being pumped around, etc.

    b) it is usually considered to be a loss of about 20% of the total power, which is of course a combination of Torque and RPM.
    Some transmissions are better than others.

    c) Thermodynamics is such a cruel mistress - you cannot EVER win, cannot just break even, and you are not allowed to get out of the game.
     

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