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Theory Of Testing
Volume 2, 9/10/04
Section 8 - Page 9
the Japanese Industry Standards (JIS), the International Organization for Standardization (ISO),
etc. SuperFlow has selected the SAE, STP, standards for the default configuration files supplied
with the dynamometers (ECE and DIN in the metric version). Because WinDyn can be completely
user configured, The correction type may be changed this to any standard of choice at any time.
See the section on “Power Correction Factors” (Section 8.5) for more details.
8.4.3 Ground Torque
Wheel torque is calculated from wheel power and Roll Speed corrected to standard conditions
using the power correction factors (SAE for CycleDyn and STP for AutoDyns). The is the torque
which the vehicle would deliver to the ground when tested in standard conditions.
8.4.4 Wheel Torque
Wheel torque is calculated from wheel power and engine speed. No corrections are applied. The
calculation is relative to the conditions prevailing on the day of the test. Although this is not the
actual measured torque applied to the ground, it is a common value used in marketing and
advertising to represent torque of the vehicle under test.
8.4.5 Corrected Wheel Torque
Corrected wheel torque is the calculated wheel torque corrected to standard atmospheric
conditions using the power correction factors outlined above. This is the torque of the vehicle when
tested in standard conditions. Corrected torque is only valid for full throttle tests.
8.5 Power Correction Factors
The power output of an internal combustion engine is significantly influenced by barometric
pressure, ambient air temperature, and air humidity.
• Lower ambient barometric pressure reduces the density of the air, thus reduces the
amount of oxygen filling the cylinder for each cycle, resulting in lower power output.
Conversely, higher barometric pressure increases power.
• Lower ambient air temperature results in increased density of the air, thus increases
the amount of oxygen filling the cylinder for each cycle, resulting in higher power
output. Conversely, higher air temperature reduces power output.
• Lower air humidity (less water vapor) leaves more room for oxygen per cubic foot of
air, thus increases the amount of oxygen filling the cylinder for each cycle, resulting in
higher power output. Conversely, higher air humidity reduces power output. Higher
humidity may also reduce the burn-rate in the cylinders.