Geekin' again

[Jon Davis]

Jay Hassinger wrote:

> Does this mean we get to call Cadle a monkey?  ;-)

First of all, I have never seen a chassis dyno personally nor have I seen
how it really works, BUT it would be silly to have a tachometer and a torque
measurement device on the drums of an inertial dyno (if you were talking
about a brake dyno, then I'm the monkey, please ignore me). The drums most
likely have a magnetic or optical pickup. The rpm of the drums is calculated
from the time between pickup pulses and the acceleration of the drum is
calculated from the last 2 rpm measurements and the time between them. The
hp at the drum can be calculated from the 1st 2 and the engine rpm is
calculated from the time between sparks. Engine torque is caclulated from
the hp at the drum and the *engine rpm* using tq = hp X 5252 / rpm because
torque at the drum is useless on the dyno chart.

The reason I say torque/tach would be silly is because very accurate timing
devices are dirt cheap (like wristwatches). Timing devices give data in a
format that is easy to use with a computer. Magnetic and optical pickups are
also accurate, cheap and robust. Tachometers and especially torque sensors
are expensive, require analog/digital conversion to work with a computer,
are susceptible to noise, and aren't robust.

Jon Davis