Peter,
That is a lot of horsepower to disappear down the drain, isn't it. Well,
there are a number of places it could be going. If you listen to some
people, there's twenty horsepower eaten up by the engine fan, another
twenty by the water pump, and so forth. I don't really believe these high
numbers either, but at least some parasitic loss is going to items like
this, depending on how the engine is configured on the engine dyno. I'm
sure Ford uses the most stripped down configuration possible to come up
with 225 HP. On the chassis dyno, you do have rolling resistance, plus some
other friction added by the rollers that couple the tires to the dyno.
Also, it's hard to equate horsepower to the torque you apply by hand. If
you don't think rolling resistance is significant, try pushing your car
around on level ground. If you measure the force it takes to just roll and
multiply by speed (with the appropriate constant for the units used), this
will give the horsepower consumed by rolling resistance. Notice that the
horsepower required is proportional to speed; that is, it takes twice as
much horsepower for a given acceleration at 60 mph as it does at 30 mph,
and so forth. Also, you can measure the amount of torque it takes to turn
the wheels when the car is jacked up and multiply by rpm, then divide by
5252 and this gives the HP consumed by the drive train. Since most of this
is probably viscous resistance which goes up with rpm, then the actual loss
is probably a lot higher. But it wouldn't take many horsepower to make the
tranny and differential oil get real hot, so I'm guessing only a very few
horsepower is actually heating the oil and bearings, etc.
I'll be curious what other people have to say about this.
TTFN,
Bob
|