How do I calculate Torque?

wrote:

> Using vehicle acceleration to measure hp is useless. We've done it
> with airplanes on takeoff, and we get a horsepower figure of about
> one-fifth of what we know the engine is giving us. Any movement thru
> air represents drag, any rolling wheels represent drag, and the losses
> through the drivetrain are significant. Further, unless the engine is
> operating at the desired RPMs (redline or max torque) it's all
> irrelevant.
> The most accurate measurements use an engine brake and
> torquemeters. Torque x RPM x 6.28 divided by 33,000 equals hp.
>
> Dan
>
True, but the original poster didn't have access to a dyno. Your
reasons are why I pointed out that all data must be taken at low speed,
and would be a hell of a job. One would need to take data about every
mph, and need some sort of automatic data acquisition system.

I should have also mentioned measuring DECELERATION also. This gives
data on drag sources. One can see the slope of the deceleration curve
change as aero drag drops off but tire and chassis drag, much of which
are independent of velocity, stay there. One should account for these
forces when computing hp or torque. However, rolling friction is
typically relatively low, so acceleration data at low speed will give a
REASONABLE value on a car with manual transmission.

BTW, data I have seen on chassis friction indicated less than 5% of
power lost there. Tires were about the same.