In a message dated 1/18/02 3:01:49 PM Eastern Standard Time,
steveis@SPEAKEASY.ORG writes:

> can you explain the
>  difference between horsepower and torque, and more importantly, how they
>  work together in your example. And, just what does this mean to me in my
>  1.9L gas Westy 4spd?
 Wow...got some time?????

You need to understand the difference between force and work.  (If I sound
like your high school teacher that's because I WAS a high school teacher..and
POOR one at that)
 Force..it's "pressure" for our purposes..it can be measured in several
ways.. Like "pounds" fer instance..great..we got pounds...what does THAT
mean?...pounds per????

mmm Ok..let's just drop that for a bit and go to torque..that's pounds
applied via a lever (and a wheel is just a continuous lever)
Force though a distance, but for torque it's a rotational thing.....NO MOTION
is required!!!..I'll bet you've done that..applied 150 ft/lbs (really
Pounds/Feet by modern convention) by standing your 150 llbs on the very end
of a 18 inch breaker bar..and the nut didn't turn...
SO...POWER is the force though a distance as a function of TIME (distance?)
...
HP is stated as 550 ft/lbs (hey,I'm old, ok?) per second...
SO...engines develop a twist at the crankshaft.. cool..how much? Well, that
depends on the engine..and things that effect engine performance (altitude?)
We're gunna talk MAXIMUM here too...obviously restricting the fuel or the air
(foot off the throttle) is going to lower the available torque.
The BIG factor is engine speed..NOT because speed is part of torque, but it's
how well the engine fills the cylinders and burns it's fuel in the time it
has to do that..
porting, cams, fuel system etc all play a part in how any type of engine
delivers torque at any given speed...
Diesels and Petrol engines differ in the way they function.. for any given
displacement a diesel will develop less total torque than a similar gas
engine (compare VW rabbit 1600 gas and diesel specs) HOWEVER the diesel tends
to make it's maximum torque quite low down on the rpm scale AND tends to HOLD
that same figure for most of the RPM range.  Like this:
RPM GAS Diesel
1000    110 130
1500    135 144
2000    145 138
2500    155 135
3000    168 135
3500    171 132
4000    170 130
4500    152 ---
5000    128 ---
5500     95 ---
GENERALLY diesel are slower turning due to the heavier bits needed to
withstand the greater pressures of diesel operation.
The gear box matches the rpm to the road speed so that you can select the
necessary RPM for the wheel torque requirements..
MANY race engines will develop all KINDS of HP...but it's low torque at some
ungodly RPM...drop down the rpm range and it doesn't do it..it will stall as
the load is higher than the available torque..