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Posted by Timberwoof on June 25, 2008, 11:40 am
In article
> > ?Today I looked at a 900 Vulcan Kawasaki cruiser. Long story short the
> > salesman said that the donk on the Kwakka ..900 V twin .. is equivalent in
> > power to a 400 cc 4 cylinder. Is that True ????????????
>
> Horsepower is a measure of the *rate* at which work is done.
>
> You can take an engine that produces 50 horsepower at a certain RPM,
> and double the RPM and get twice the horsepower.
Uh... Let's clarify that a bit.
If you use a gearbox to change the rate at which the shaft spins, then
you also change the torque, but the power remains constant (minus, of
course, losses to friction.)
As long as the engine's torque curve (that is, the function of maximum
torque output for a range of RPMs) is flat, then what you say is true.
However, it rarely is.
> OTOH, you can compare a 400 cc engine that turns twice as fast as an
> engine twice the displacement, and the smaller engine will equal the
> larger engine's horsepower.
Well, not necessarily either. It all has to do with how much torque the
engine puts out. My little Honda CB-1 had a 400cc engine; it typically
ran at about twice the speed of my big R1100GS engine. However, at any
engine speed, the R1100 would put out about twice the maximum torque and
thus about twice the power over its range as the CB-1.
Curly, it really ultimately comes down to the power-to-weight ratio.
--
Timberwoof <me at timberwoof dot com>
faq: http://www.timberwoof.com/motorcycle/faq.shtml
Ten Steps to Fascism: http://www.guardian.co.uk/usa/story/0,,2064157,00.html
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