Page 3 - Combined_57_OCR

Performance of 1969 Dodge Charger 500 at Daytona International
Speedway

Discussion (cont•d)

One interesting fact disclosed by the data on the track design
is that the track length Actually 13200.076c}_ is measured at the out­
side rail, unlike Indianapolis which is measured 5 feet from the in­
side edge of the track. As a result a car that could run right at
the inside white line of the track would run 251s less than the 2.5
mile lap distance, or a saving of 1.9% in distance traveled. More
realisticly a- car staying in the center of the first lane would
travel only 2.458 miles per lap, while a car staying in the center
of the top lane for a complete lap would travel 2.494 miles per lap.,
a 1.45% greater distance. As a result a car traveling at the same
actual road speed in the bottom lane would have a timed laps speed
about 2.6 mph. higher that the car in the cop lane.
Figure 3 shows the power allocation for the race car for this
one lap. The engine power available is plotted as well as the power
required broken down into rolling resistance, air resistance and tire
yaw drag. The power available is based on the power run made on the
engine from car #046 after the test. This power is corrected for the
actual weather conditions existing at the time of the particular test
and for the estimated effect of the ram air at the carburetor. It
will be noted that the power available is almost constant, remaining
between 572. and 532 for the entire lap. The tire rolling re­
sistance is calculated based on the total normal force acting on the
car and the car speed. The equation used is believed to be correct,
but no test data is available to substantiate it. The rolling re­
sistance varies between 43 and 118 HP, and so is a relatively small
factor in the overall car performance. Very little can be done about
rolling resistance,- since with everyone using the same tires, any
reduction in. rolling resistance will help the competition as well.

The air resistance shown on the curve H* C O the estimated air re
sistance for the entire lap., taking into account the actual air
density at the time of the test and the effects of the wind that
existed during the test. rhe data seems to indicate that there was
a headwind of about 12 mph. on the back straight. There was no wind
through the number 3 and 4 turns or on the straight from the number
4 turn to the tri-oval turn. On the straight between the tri-oval
and the number 1 turn the data indicates that there was a loss in
acceleration equivalent to a 6 mph. headwind. It is possible that
the wind blowing around the grandstands and banking could reverse
direction in this area, and it is also possible that the' side wind
effect on the car in this section could cause the car to yaw and
increase its drag. A third possibility is that the driver running
c the wall could have incra.. r adynamic drag in this
section. There is not enough data available to explain the reason,
but the total power required along this section of straight is higher
than expected, and is accounted for as air resistance in the curve.
The wind effects through the number 1 and 2 turns is as expected,
with the headwind effect increasing as the car goes through the turn.
The resultant calculated aerodynamic horsepower varies between 290
and 4 - based on the m coeificient of car #046, "tlie
car speed and the assumed wind conditions. Without the wind the
aerodynamic hors (Mower would vary between 290 and 385 HP for the