G-Tech Hp Meter Update

[Bruce Bowling]

> 
> You are correct that it is horsepower delivered at the wheels
> minus rolling and aero losses.  There is no correction figure
> available for frontal area and coeficient of drag or friction.
> 
> Because of all these things I think is is a OK as a qualitative
> tool, but lacks as an absolute quantitative tool.  You can
> still see instantaneous HP versus speed or RPM.  However, that
> means keeping one eye on the meter, which is not ideal.

It will work as a qualitative tool only if comparisons are done
at the same environment, or one corrects for the environment. 
In other words, one can perform *relative*
comparisons only if performs all of the testing at the same temperature, 
barometer, or humidity, or compensates.

To see the effects, here are some numbers:


Assume I measure 250 horsepower at 6000 RPM,by some method 
(G-meter, dyno,etc). This measurement was taken at some test
temperature, humidity, altitude, and barometer. It is desirable
to correct to some "common" temperature,barometer, and humidity
that everyone agrees to. The two common ones are Standard and
SAE corrections.  Standard Correction is at 29.92 Inches Hg 
Barometric pressure at sea-level, 0% relative humidity, 
and 60 degrees F. 

The numbers below were are
all corrected to this "standard" environment:
Data taken from     http://devserve.cebaf.gov/~bowling/stdcorr.html

TEMPERATURE TEST - Baro-29.92, Rel humidity=0%
Engine: Small Block Chevy 350
Temperature       Corrected HP
(Farenheight)
-------------------------------
20                236
40                243
60                250
80                257
100               264

Remember: Engines produce more power when the temps are colder,
and the correction compensates, so cold temps correct the 250 HP
to a lower number (what the engine would produce at 60 degrees F)

BAROMETER TEST - Temp-60, Rel humidity=0%
Engine: Small Block Chevy 350
Barometer         Corrected HP
(Inches Mercury)
-------------------------------
29.00             261
29.50             255
29.92             250
30.20             247

HUMIDITY TEST - Temp-60, Barometer=29.92
Engine: Small Block Chevy 350
Relative          Corrected HP
Humidity (%)
-------------------------------
0                250
50               253
100              256

> 
> It still may be the best thing available today, and easier to
> use than a stopwatch.  I suspect the braking and cornering
> functions are less problematic.
> 
> paul timmerman
> 

And the price is good, too!

- 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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