Engine dyno for EFI project

[Jonathan R. Lusky]

Ed Lansinger writes:
> Dave Morrill wrote:
> >Does anyone have any tips or plans on how to build an engine dyno? 
> >...
> >I initially began thinking about using a disc brake for a load...
> 
> Of course, that's what early dynamometers were, a brake, giving rise to terms
> such as "brake horsepower".
> 
> I'm not saying you can't do it, but I was part of a quick experiment once
> to do just such a thing.  I would recommend against it unless you are willing
> to put in some serious engineering analysis and development.  For that effort
>and expense you'd be better off buying a water brake dyno as Anthony suggested.

The problem is that all of that absorbed energy has to go somewhere--
And its going to go there as heat...   trying to absorb 200+ HP, I'd
guess youd about 30 seconds out of a typical set of pads and a rotor.
 
> If you are willing to live with that level of inaccuracy, then it seems to
> me that in-vehicle tests will give you what you are looking for (I assume
> this is for a vehicle of some sort).
 
Real timeslips from a dragstrip are VERY useful for high end tuning.

> >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?
> 
> Measure the mass flow rate and the temperature rise across the water brake.
 
Ick, way too inaccurate and too complex.  Mount the absorber so that the
whole thing can spin.  Attach a bar that projects radially.  Use a
linear force measurement device to hold the other end of the bar.  A
heavy duty spring scale will work, a steel bar with a strain gauge is
preferable (and is what most commercial dynos use).   

Really high end commercial dynos will have a "torque cell" between the
engine and the absorber.  The torque is a shaft supported on bearings,
with strain gauges on the shaft and slip rings to make the electrical
connections.  Pretty accurate, very high dollar.

> There are machine shops that will rent dyno time.  That is probably the best
> way to go in terms of safety and low capital investment.

I've never verified this, but I've heard that used double roller 250HP
water brake chassis dynos go for around $2k.  These things are pretty
good for dialing in fuel/spark up to about 200 HP (rear wheel).  


-- 
Jonathan R. Lusky                        lusky at knuth.mtsu.edu
http://www.edge.net/~lusky/                 (615) 726-8700
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68 Camaro Convertible - 350 / TH350  \_/ 80 Toyota Celica - 20R / 5spd