->The hydraulic pump approach is intriguing. I wonder how much pump
->you'd need to soak up 500 ft/lbs? You have to be able to take
->everything WOT has to give at a specific RPM (and hopefully hold it
->there for accuracy). I also wonder what the rpm limits are for the
->pumps. The load could be increased by increasing the pump back
->pressure, but by how much before something fails?
->
Keep in mind a simple dyno is basically a device for measuring energy
output. You have to *DO* something with that energy. Increasing the
pump backpressure raises the temerature of the fluid and of the
surrounding valves, pumps, etc. Some of the older dynos were used to
boil water, run fans, heat air, pump water, etc are energy dumps.
Instead of thinking of it a 500 ft/lbs, think of it in terms of Watts.
units tells me:
lucas% units
you have: hp
you want: watts
* 7.456999e+02
/ 1.341022e-03
So say you're dynoing a 200 Hp Production engine (certainly reasonable)
you're looking at what to do with 15Kw. Lotta heat. (let's not get into the
BHP vs SHP discussion, I'm doing engineering approx here :-}) Turn it around
and look at a 500Hp V8 and the numbers get BIG. Now I know how to dissapate
that kinda heat, and they're doing at Newark Airport right now with a few
hundred tons of snow, but I don't think you want it in the garage.
Most hydralic pumps are fairly low RPM devices. Hundreds to low
thousands as I recall. Keep in mind you're moving something (hydalic
fluid) with a relatively high viscosity, which will break down over
time due to the shear in the pump and elsewhere. At higher velocities
it will cavitate as I recall. Selection of the fluid would be
critical.
And if you plan to gear the output down to drive such a pump you'll
have to take into account the efficiency of the gearbox. Typical
efficiency of automotive gearboxes for example, are not as high as you
would think. I don't remember exact figures, but the numbers 70% and
80% for automagics and 80%-85% for manuals stick in my mind. And those
efficiencies will change over time, ambient temps, and lubricant temps,
all of which are less than constant. Think about how hot your trans and
diff get. It's not just the proximity to the exhaust.
The criteria for building dyno's are many and critical to get
consistant repeatable measuments. If it was easy, you'd see on in the
Harbor Freight catalogue.
->If the engine development program doesn't work out, I'll bet a pump
->that large could also be rigged up to do double duty as a car crusher ;-)
->
A constructive energy dump....:-}
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