Page 2 - Combined_38_OCR

H. P. Bruns - 2 - October 9, 1969

Static pressure only was measured at two locations in the plenum; one probe (Pgl)
was located at the immediate upstream entrance to the plenum, the other (Pg2) was adja­
cent to the carburetor entrance section. Table II lists the recorded values.

Analysis of the first series of test data, Table I, show it to be highly erratic in
most areas with no definite trends apparent. The second series of tests, Table II, where
Ps only was measured indicates a more stable measurement. However, few positive con­
clusions can be drawn in regards to duct efficiencies since great aerodynamic flow differ­
ences exist between the Charger 500 and the Charger Daytona. An attempt was made to
collect the data at the same engine RPM values for each condition, but due to the configu­
ration differences, track and wind conditions, the carburetor throttle position was not
always the same. This probably accounts for the erratic readings shown by Table I values.

During an earlier test series on the Daytona Charger where the 3.5 inch cowl inlet
scoop was being used, the engine exhaust pipe color showed a significant change during a
brief 11/2 lap run at Daytona. Since carburetor air/fuel ratio characteristically goes
leaner as air density increases, some indication of carburetor inlet pressure change, if
significant, could be observed through a plug analysis. With this in mind WOT plug checks
were made on the NACA inlet and on the optimum cowl inlet. These plugs were sent to the
Engineering Office for evaluation. However, to date no results have been received regard­
ing these plug checks.

Significant gains in engine horsepower can be achieved through proper ducting of
air to and through the carburetor. Development of ducting should ideally be performed
under more controllable conditions such as the engine laboratory in parallel with prop­
erly controlled wind tunnel tests. It is extremely important in such tests to be able to
investigate the entire system and not just an engine or a duct. Aerodynamic flow of a
system such as an automobile can be significantly affected by engine air flow character­
istics , carburetor ducting, and location of inlet on the body as well as contours and shapes
of the body and ducting. All must be optimized within the given constraints if any signifi­
cant improvement is to be gained. All subsystems must be thoroughly understood either
analytically or empirically in order to design follow-on body-engine system ducting.

These track tests were extremely limited in instrumentation (1 each 36-inch
manometer) and a vehicle restricted to 160 MPH speed due to poor mechanical conditions
and absence of a clean aerodynamic front end (not standard Charger 500). From this
experience it is felt that with a reasonably good aerodynamic vehicle, good instrumentation
(now available at nominal cost) and careful test planning and preparation we can obtain
positive high speed results at the track to supplement wind tunnel tests and/or dynamometer
testing. These types of tests performed in parallel with regular race car performance
tests on a non-interference basis can be achieved at nominal or minimum costs.

W. P. Wright

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