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position (see Figure 2). (Since sheet metal attachment at the firewall is the same for
both the FR-23 and the FW-23 and the FW-23 front end presents a tighter profile, it
was decided to use FW-23 fenders and hood on the FR-23 body for race purposes.)
The extension shows considerable droop to the top surface with the lower surface being
almost flat. The configuration tested maintained a 45 sq.in. cooling inlet opening
which is deemed sufficient for race purpose. For the street version the inlet can be
opened to twice this size but with a substantial drag increase (see Reference 1).
Figure 7 shows the aerodynamic changes to the car caused by the addition of the 18"
extension only. Approximately 44% of the total drag reduction obtained for the recom­
mended configuration is seen to be due to the nose shape. The shift in the wheel lift
pattern again indicated a rearward shift of the C.P. while the side forces show a slight
forward movement in their C.P.

On the Dodge Charger the nose angular mounting had some beneficial effect on
aerodynamic drag (Reference 1). This was not the case for the proposed Plymouth nose
shape (Figure 8). Some alteration of the wheel lift distribution can be made (Figure 8(b))
by the angular orientation of the nose but, as will be shown later, the same effect can
be obtained by proper spoiler design.

Figure 9 presents the results of studies conducted to locate the best spoiler
position. During this investigation the spoiler thickness was varied at each body rake
angle so that the bottom surface of the spoiler was always at NASCAR minimum clear­
ance. Therefore, the spoiler used at a body rake angle of zero degrees was a thicker
spoiler than one used at a rake angle of -2.5°. All spoilers were raked forward at a
45° angle relative to the sheet metal surface. Figure 10 shows the variation in aero­
dynamic parameters obtained if a constant thickness spoiler is used as opposed to the
variable thickness spoiler. The lower drag and higher lift values obtained with the
constant thickness spoiler at the higher rake angles results from the constant thickness
spoiler exceeding NASCAR minimum clearance values at the higher rake angles. If the
spoiler thickness is held constant and the entire car is raised to the point where the
spoiler is legal, higher drag values are obtained (see Figure 11). Therefore, it is
better to keep the entire car as close to the ground as possible and at the same time
keep as large a front spoiler as possible.

The best location for the spoiler is seen to be approximately 12 inches aft of the
nose leading edge. Some leeway is available in the spoiler position since little change
is seen in drag as the spoiler is moved from 10 to 23 inches aft (see Figure 9(f). The
greatest change occurs in the distribution of the lift forces, therefore, giving some
control over handling characteristics. The undernose spoiler contributes approximately
30% to the overall drag reduction.

Alteration of the backlight adds the additional 2£% to the overall drag reduction,
See Figure 12. The semi-fastback backlight is a smooth gradual slope stopping at the
rear deck lid opening, (Figure 4). The fastback backlight (Figure 4) slopes to a point
midway back on the trunk lid. The incremental aerodynamic advantage gained by using
the fastback instead of the semi-fastback is not considered enough to warrant the addit­
ional car body rework required to obtain the fastback configuration.

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