Page 2 - Combined_132_OCR

page 2.
Results of Daytona Tests of the 1968-^ Plymouth Race Car.

Discussion (cont'd)

3.07 axle ratio was satisfactory with the single 4-bbl. carbureted
engine in February due to the lower peaking speed of this engine.

A very important factor is weather. Listed below are the conditions
on the qualifying day for the February race and the time when the 184
mph was run:

Date 5/17/68 2/11/68

Temperature
Humidity 68% 56%
Barometer 29.94 in.Hg. 29.83 in.Hg.
Weather Sunny Overcast

This weather difference is responsible for two factors of lap speed
reduction, power loss and tire bite reduction. The higher temperature
and greater humidity result in a power loss of over 3% and a reduction
of about 1.1 mph in lap speed. An even bigger loss in lap speed is due
to the effect of track temperature on tire bite. In February the track
temperature was probably around 60° since the day was heavily overcast.
In May track temperatures of up to 137 were measured. The increase in
track temperatures has a very significant effect on lap speed. We have
no test data on this, but Goodyear records show an average difference
of about 3 mph for the same tires on the same car between February and
July. About 2 mph of this difference is apparently due to the differ­
ence in tire bite.

The corrections'for axle ratio, engine power loss and tire bite
loss would raise the equivalent February lap speed of this car to 187-
187.5 mph, and this is on the same type Goodyear tires used in the race.
The special Goodyear qualifying tires used by all of the faster cars in
February will add about 1.5 additional mph to this lap speed, bringing
the speed up to the 188 to 189 mph bracket on the basis of February
conditions. It is possible that another 20 horsepower will be available
from the sump manifold before the July 4 race, which would be enough to
raise the car up to 190 mph with the February weather conditions, or
about 187 mph under weather conditions as existed during the test. Also
not tested during this test due to the engine failure were the reinforced
wheels. It is expected that the reinforced wheels will add 1.5 to 2 mph
to the Daytona lap speed. The reinforced wheels are not legal under
current NASCAR regulations.

The 1968-^ Charger race car should be about 1.5 mph faster than the
Road Runner, based on Proving Ground tests. The proposed new grille for
the Charger should add an additional 1.5 to 2 mph to this speed, so that
under similar weather conditions to the Plymouth test the Charger should
run 187 to 188 mph with race tires, and might exceed 190 mph with the
qualifying tires and the reinforced wheels if lift problems do not cause
handling difficulties.

G. M. Wallace
GMW/mh

cc: R.D. Engle, C.D. Moore, J.D. Pointer, L.J. Rathgeb, W.C. Tiahrt