Engine dyno for EFI project

[Bruce Bowling]

~ 
~ Hello,
~ 	Does anyone have any tips or plans on how to build an engine dyno? 
~ Before I start my efi project I want to build a dyno so I can benchmark my
~ results and debug the system in the shop.  
~ 	I initially began thinking about using a disc brake for a load, and
~ measuring the torque-losses on the pad to get an approximate torque measurement
~ Even had a method to calibrate w/ a torque wrench.  The numbers would not be
~ exact but at least I would be able to see relative improvements as I made
~ changes to the efi system.
~ But then I though about a cast iron disc spinning at >7000 RPM and did not feel 
~ like this was very safe, heat and wear would be significant probs as well,
~  - any comments ?  
~ 
~ I guess the industry uses a water pump for a load, I'm not sure how to do the 
~ calculations, do you use water pressure as a measurement, flow rate of
~ liquid?  What method could be used to calibrate?  Any advice on where to get an
~ applicable pump?
~ 
~ thanks,
~ 	Dave.
~ 
~ 	
~ 

I had an idea a while back, but never followed up on it.  Why not use a
calibrated alternator for a load device?  For instance, when you turn
on the headlights, the engine RPMs drop down a small amount.  This
drop is caused by the alternator "sucking" up some of the total
energy delivered by the engine.  If one kept a constant current
draw on an alternator, a table of rotational torque vs. RPM can be created.
Even easier if one wants only relative power improvements:  make 
switchable load that can be electrically switched on and off the 
alternator (ie. alternator has either no load at all, or a fixed
electrical load), at at a given no alternator load RPM, switch
on the alternator load and watch the RPM drop and save this drop.
Now, after a engine modification, repeat the above - better engine
power means lower delta RPM (I think).

- Bruce

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               Bruce A. Bowling
  Staff Scientist - Instrumentation and Controls
 The Continuous Electron Beam Accelerator Facility
    12000 Jefferson Ave - Newport News, VA 23602
                 (804) 249-7240
                bowling at cebaf.gov  
        http://devserve.cebaf.gov/~bowling
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