Page 1 - Combined_132_OCR

INTER COMPANY CORRESPONDENCE

FILE DATE
May 22, 1968
CODE
TO - NAME DEPT. DIVISION PLANT/OFFICE
H. P. Bruns 7590 Engineering Highland Park
FROM - NAME DEPT. DIVISION PLANT/OFFICE
G. M. Wallace 8930 Engineering Highland Park

SUBJECT:
RESULTS OF DAYTONA TESTS OF THE
1968-^ PLYMOUTH RACE CAR

Results

As a result of the tests conducted with the 1968-^ Plymouth Road
Runner race car at the Daytona International Speedway from May 13
through May 18, 1968, it appears that the car has a speed potential
of 188 to 190 mph when corrected to the weather conditions experienced
during the month of February. As shown by the previous Proving Ground
tests the optimum car rake angle for best lap speed is 2-3/4°, equal
to approximately 6" of rake measured over the wheelbase.

Discussion

During the testing of the 1968-^ Road Runner race car at Daytona
one of the major goals was to find the optimum rake angle for the car
to result in the lowest drag and highest lap speed. The car was de­
signed for a rake of four inches measured over the wheelbase, and was
tested at four, five, six and seven inches rake. The actual rake was
measured with the angle of the top of the driver's door, since the re­
worked sill could not be used for an accurate measurement. The chart
below lists the speeds obtained at the various rake angle as well as
the drag measured at the Proving Ground for a 1968 standard Dodge
Coronet race car. The Proving Ground drag data is given in CdA, drag
coeificient times frontal area, with a lower number indicating lower
drag.

Rake - inches Rake - degrees Lap speed at CdA - measured at
at wheelbase Daytona - MPH Proving Ground

1- 3/4° 180.0 mph 10.8

2- 1/4° 183.0 mph 10.5
ID
2-3/4° 184.0 mph 10.2
kD
7" 3-1/4° 182.5 mph 10.7

As indicated by the Proving Ground tests the 2-3/4° rake is the
optimum for the 1968-lj Road Runner.

The 184 mph lap speed for the Road Runner with the optimum rake
seems slow compared to the speeds run in February, but this must be
corrected for several differences. One factor shown in the tests was
axle ratio. All of the testing with the different rakes was done with
a 3.07 axle ratio, which allowed 6600-6700 maximum rpm. Later the
ratio was changed to 3.18 which resulted in a gain of at least 0.5 mph
by allowing the engine to reach a maximum rpm of about 6900. The 3.18
axle ratio was not run with the 2-3/4° rake due to engine failure. The
84- 1 10-7879 REV. 1-63