Gary Wolf wrote:

Norm,
   An oil pump seems at first to be an easy choice to absorb horsepower but
there is a problem in that the temperature determines the viscosity of the
oil. Water remains the same until it boils. The problem with both is to
convert the output into a measure of horsepower.
   A water dyno has an impeller like a pump but the housing is ribbed
internally so that the rotational force is transmitted to the housing. The
dyno is supported in bearings on its shaft and the housing would like to
rotate when water is introduced into the housing, but this rotation is
restrained by an arm thet bears onto a glorified bathroom scale. The length
of the arm x the force measured on the scale gives the torque. The rpm is
measured from the shaft.
   You could use oil instead of water in this absorption unit but it would
be difficult to get a stable reading if the temperature were rising. I have
seen inexpensive go-kart dynos that use oil but they have a circulating pump
and rad, and even then don't work as well as a water unit.

                                                                Gary Wolf

 
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