Dynojet WinPEP 7 - Manual (Page 18)

WinPEP 7 User Guide
C H A P T E R 2
How Your Dyno Works
2-2
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HOW YOUR DYNO WORKS
Dynojet’s inertia dynamometer (dyno) is a measuring device for recording and
displaying power and torque of an engine. Its method of measurement directly
implements the engineering principles of power and torque. Correction factors assist
in the comparison of these measurements under various test conditions, making
computer hardware (your dyno electronics) and software (WinPEP 7) necessary to
obtain, interpret, and display the data.
H ARDWARE AND S OFTWARE
The dynamometer electronics acquire data, from the spinning dyno drum, necessary
for power, torque, and correction factor calculations. This includes air temperature,
absolute barometric pressure, humidity, drum timing, and engine
RPM .
During a run, the data is stored in the dyno electronics memory.
After a dyno run is finished, data from the dyno electronics, calibration data, and user
notes are saved to a file on the computer’s hard disk. When you use WinPEP to select
a run, the data is loaded from the hard disk into computer memory. Data from up to
twelve runs can be viewed in WinPEP at once.
The information collected can be used for viewing
horsepower and torque graphs .
Data can either be viewed as measured (“uncorrected”) or corrected to standard
atmospheric conditions using WinPEP.
T HEORY OF O PERATION
P OWER
Power, in mechanical terms, is the ability to accomplish a specified amount of work in
a given amount of time. By definition, one horsepower is equal to applying a 550
pound force through a distance of one foot in one second. In everyday terms, it
would take one HP to raise a 550 pound weight up one foot in one second. So to
measure horsepower, we need to know force (in pounds) and velocity (in feet per
second).
Dynojet’s inertia dynamometer measures power just in this way. The dyno calculates
velocity by measuring the time it takes to rotate the heavy steel drum one turn. The
dyno measures force at the surface of the drum by indirectly measuring the drum’s
acceleration. Acceleration is simply the difference in velocity at the surface of the
drum from one revolution to the next. The force applied to the drum is calculated
from acceleration using Newton’s 2nd law, F=MA, (F)orce equals (M)ass times
(A)cceleration.
Power is coupled to the drum by friction developed between the driving tire of the
vehicle and the knurled steel surface on the drum of the dynamometer.
T ORQUE
When an object rotates around a point, the object’s speed of rotation depends on
both an applied force and the moment arm. The moment arm is the distance from the