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or
a variable load that maintains a preset engine rpm or vehicle
speed. This feature is ideal for forcing the vehicle to
operate at certain loads for tuning. The Dynojet can also
measure air/fuel ratio while testing.
Mustang
The
Mustang chassis dyno uses an Inertia load as well as an eddy
current brake load to simulate the "actual” load
(combined aerodynamic plus rolling frictional load) that the
vehicle would experience when in motion.
Notice in the photos how the rear wheels sit between two
smaller 10.7-inch diameter rollers. There has been some
discussion about the tires getting "pinched" between
the rollers and creating more rolling friction, but no
substantial evidence of this could be found. However, Mustang has a dyno (MD-1750) with a single 50-inch
diameter roller per wheel that alleviates the wheel-pinch
concerns. The internals of the Mustang dyno are composed of an
eddy current brake to provide a variable load and an inertial
disc to provide a fixed load.
Mustang claims because its dyno loads the vehicle as it
would be on the road, you can perform 0-60
mph,
0-100 mph,
and quarter-mile measurements
on its chassis dyno. Speed Nation has obtained quarter mile
times within 0.1 second of actual runs at the track. We're not sure how the launch dynamics are simulated on the
Mustang dyno, which |
includes
weight transfer, acceleration, jerk (the derivative of acceleration
- how fast the acceleration occurs) and some other variables. The
Mustang dyno can also measure the air/fuel ratio while testing.
CorrectIon
Factors
Correction
factors are used by both dynos to account for varying atmospheric
conditions such as temperature, pressure, and humidity. The
measured horsepower and torque are multiplied by the correction
factor to obtain the corrected values. This is similar to the corrected
times and speeds provided by some quarter mile tracks. Theoretically, you can dyno on a hot day in the high altitude
of Denver and on some other cool day at sea level and produce the
same corrected horsepower even though the observed horsepower you
are producing at each location is different.
Both dynos calculate a correction factor based on a
Society of Automotive Engineering document (SAE-J1349).
When testing was performed on the Dynojet, the correction
factor was 1.10, which means the observed numbers were multiplied
by 1.10 (adding 10 percent) to get the corrected values. The
correction factor for the day when testing was performed on the
Mustang dyno was 0.9595 (removing 4.05 percent). The correction
factor when road-testing at
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Keystone
Raceway was 0.962, a correction reduction of 3.8 percent.
Testing
Testing
was performed on each dyno using a '00 six-speed Z28 Camaro.
We measured the horsepower and torque versus engine rpm in
Second, Third, and Fourth gear.
The test data also included how fast the engine accelerated
in Second and Third gear (in rpm versus time) to be compared
with actual road tests to assess each dyno's loading of the
drivetrain. After
each individual test we let the engine coolant temperature as
displayed by our AutoTap OBD-II scanner to read between 200 and
205 degrees F for consistency.
Dynojet sent out a representative to Strope's Speed Shop to
verify calibration and witness testing.
Calibration for the Dynojet is just a matter of verifying
that the computer's configure file has the proper load-roller
inertia factor. There are no manual calibrations for the Dynojet.
The
road tests were pertorrned at Keystone Raceway to provide a level
surface to measure the vehicle's rpm versus time in Second and
Third gear using AutoTap. Chad Fellabaum of C&C Racing in
Pennsylvania weighed the car so the exact weight could be used for
the Mustang dyno loading to be compared with the road tests.
The
dyno curve charts show horsepower and torque versus rpm in Third
gears for both chassis >>
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