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1968 Dodge Charger 500: official report on speed tests


The following is a verbatim transcription of a report made on December 9, 1968. The text comes from a document provided by Greg Kwiatkowski, the header of which is shown above. Allpar has not changed the wording but has added some paragraph returns and images for easier reading.



As the results of the testing of the prototype 1969 Charger 500 race car at the Daytona International Speedway it is felt that the car as tested should be a competitive race car with a good chance of being successful.

The performance of the car is superior to the 1968 Fords and Mercurys with respect to both speed and handling. In addition to the high speeds obtained useful data was also obtained about other facets of the overall performance of the race car.


From November 25th to 29th, 1968 the newly built prototype Dodge Charger 500 race car was tested at the Daytona International Speedway. The driver was Buddy Baker for all of the tests.


The highest speed obtained during any of the tests was 192.27 mph, and at this speed the driver found the car to have excellent handling and to be very controllable. This is 6.1 mph faster than the run during the September test at Daytona with car 046, the 1968 Charger converted to a 1969 Charger 500 body configuration. The major factors involved in this increase in speed are: different ties, greater engine power, underbody to body angle, bracing bars in engine compartment, heavy flywheel, wider rims, reducing the air flow to the radiator and weather differences. The effects of these individual items are covered in detail in the discussion.


Other items were also investigated for their effects on speed such as axle ratio, exhaust pipe ends and from spoiler length. A series of tests was run to determine the effect of changes in engine power to lap speed, and preliminary results indicate that in the 190 mph range it takes 17.5 horsepower to increase the lap speed one mph. A correction factor system was developed that appears to come fairly close to correcting for the effects of weather changes on lap speed on the Daytona track. This is also discussed later.


During the test, the baseline condition differed from the best run of car 046 during the September test in several respects.

The body shells of both cars were 1969 Charger 500s with the fastback backlight. Car 046 was built with the floor pan parallel to the body, while the new car was built with the floor pan at an angle of 1.5° to the body due to the drag reductions shown for this configuration in the wind tunnel tests. The engine in the new car is mounted lower in the car since it is designed to be run with a dry sump system. For this test a normal wet sump oil pan was used, with the bottom of the pan being below the legal minimum clearance.


Both cars were run with the same car height as measured at the sill. Both cars ran single carburetor ram manifolds, although the new car had the new design air cleaner and a different advance curve in the distributor. The engine from the new car has not been checked on the dynamometer as yet, but it is estimated to be about 10 horsepower better than the engine that was in car 046.

The September test was run with Firestone tires of the same type as used in the July 4th race. This test was run with Goodyear tires that they say are the same as their July 4th tire, although the tires had no compound identification on them.

The bracing bars that bolt in across the rear corners of the engine compartment were not installed in car 046 for the September test, but were in the new car.


For a baseline condition both of the cars had the grille completely blocked with tape, with all of the air for the radiator coming in through the hole under the bumper. On car 046 the air for the oil cooler came in through this same opening, while on the new car the oil cooler air comes in through the left inboard headlight opening.

Car 046 ran with a 2.94 axle ratio, while the new car had a 3.07 axle ratio in baseline conditions. There were also differences in weather conditions between the two tests.

A correction factor has been developed that appears to make a rather good correction for weather differences, so to remove this variable, all of the speeds and speed differences will be given corrected to 29.92" Hg [inches of mercury] dry air and 60°F unless otherwise stated. The correction factor will be discussed in detail later in the letter.

The corrected speeds are representative of speeds that should be obtained with weather conditions that were encountered during the first week of practice in February 1968. The corrected best speed obtained on car 046 in September was 189.02 mph (186.18 mph observed). The baseline speed for the new car is 191.34 mph for an average of several runs (188.8 to 189.7 mph observed speeds). This gives an advantage of 2.32 mph for the new car over car 046. An approximate breakdown of this difference is:

Goodyear tires instead of Firestone+ .94 mph
Engine with 10 HP more+ .55
Engine compartment braces in place+ .31
3.07 axle ratio in place of 2.94- .21
Underbody angle and other changes+ .73
+2.32 mph

With the exception of the underbody angle each of these differences was evaluated in a separate test. The differences shown above can not be considered as exact, but the general levels are believed to be valid.

To improve the speed of the car above the baseline several changes were tried. The successful ones were:

Baseline speed191.34 mph
Reducing air flow through under bumper opening+ 1.80
Heavy flywheel+ 0.76
9" wide rims+ 0.20
(192.27 mph observed)194.10

Several other items were also investigated that did not help with the speed of the cars. These were:

Uncovering the grille- 2.60 mph
Long front spoiler (4" ground clearance)- 0.96 mph
Exhaust pipe ends cut off square- 0.61 mph

The major ones of these items effecting the speed of the car will be discussed below.


One major factor that does not show up directly in the speed numbers is the handling of the car.

Buddy Baker was never completely happy with the car 046, and found it difficult to control and very susceptible to winds. With the new car he found the car very easy to drive at all speeds including the maximum, even with considerable wind. He thought that he could race the car at 192 mph, the only limitation would be the tires. The tires used were good for only 2 or 3 laps at these speeds before they would get too hot and start to lose their grip.

This very good handling is a very great difference from the Fords, which both from appearance and drivers comments were very difficult to control at 188 to 189 mph qualifying speeds. The handling of the new car was so good that when the speed was slowed down to 187 mph, Buddy complained that it was boring to drive.

The only factor tested that had a direct effect of the handling was the removal of the bracing bars in the engine compartment. This was done as a blindfold comparison with the bars in, out and back in again without the driver knowing what changes were made. In addition to the speed differences shown, the driver noticed a definite difference in the handling of the car, with a noticeable deterioration with the bars removed. The speed loss was .38 mph and .24 mph for the two tests.

In addition to the bars in the engine compartment there are other factors that may affect the handling of the new car compared to car 046. One factor is the underbody angle, which may have an effect on the aerodynamic stability of the car. Another factor may be the new steering gear mount, which is much more rigid than the previous design. There are many other differences between the 1968 and 1969 race cars that may have an influence on the improved handling of the 1969 design.


The basic aerodynamics of the Charger 500 continues to be very good. The air inlet area through the grille and under the bumper is the area where the most can be done to reduce the drag of the stock body. The speed is increased by 2.60 mph by completely blocking the main grille, another 1.80 mph can be added by blocking most of the under bumper opening and leaving a slot of 30" x 1" just above the spoiler. The oil cooler inlet was also restricted in this final condition. This results in high but not excessive oil and water temperatures, but with the lower opening open and the grille blocked the temperatures are low.


Blocking the grille and reducing the opening below the bumper reduces the drag of the car by about 14%, or is equivalent to about 77 HP. While the rules prohibit such blocking, very similar results should be obtainable by using fine mesh screen suitably prepared.

An indication of the very low drag of the Charger 500 package is that during the horsepower per mile per hour testing the car would still lap at an observed 181.5 mph with a small carburetor that reduced the engine power to about 440 hp, less than the later track racing wedge engines.


A longer front spoiler was tested to see if it would improve handling or increase speed. This spoiler was 4" from the ground rather than the 6.5" of the normal spoiler. This long spoiler reduced the lap speed by .96 mph, and did not seem to have any important effect on handling. The suspension travel measurements indicate some reduction in front lift, but this did not show up as an important change in handling.

Uncovering the front grille seemed to increase the front lift to some extent, based on driver comments.


To show the difference between the Goodyear tires used in this test and the Firestones used in the previous test, a set of the Firestones was obtained and run. The Firestones proved to be .94 mph slower than the Goodyears.

A comparison was also made between the Goodyear tires mounted on the 8.5" rims that have been standard until now, and the same type Goodyears mounted on 9" rims. This comparison was run twice, and showed .51 mph the first time and .20 mph the second time.


A heavy drag racing flywheel was installed on the engine in place of the standard flywheel, and resulted in a speed difference of .76 mph. The heavy flywheel had an inertia of .1824 slug feet squared and weighed 38 pounds, compared to the standard flywheel (which weighs 19 pounds and has an inertia of .0937 slug feet squared). There is no immediate indication of why the flywheel does improve lap time, although this has long been considered a speed secret at Daytona.[email protected]Engine speed was recorded during these runs as with all of the runs made, but preliminary study does not show any change in engine acceleration between the two flywheels. This will be investigated further and reported on later, but the test results do indicate a definite advantage for the higher inertia flywheel.

Axle ratio

The car was originally built with a 2.94 axle ratio, but this was changed to a 3.07 ratio after the first few runs. This resulted in a loss of .21 mph in lap speed. Since the difference was so small the ratio was not changed back. The axle ratio change resulted in an increase of about 300 rpm across the board, and apparently reduced the average engine power output over the speed range. This can not be answered completely until a power curve is available on the engine as it was installed in the car.

The rpm spread from minimum to maximum averaged about 550 rpm, which is about the same as in the September test, even though the lap speeds were higher.

Exhaust Pipes

The ends of the exhaust pipes on the new car were cut parallel to the centerline of the car. For one test short extensions were welded onto the pipes to give ends that were perpendicular to the pipes. This change reduced the lap speed by .61 mph. Since such a small change in pipe length would be unlikely to represent a change of 10 HP due to exhaust tuning, this must be caused by the air flow and pressure conditions at the ends of the pipes.


There has always been a question as to how many horsepower it takes to increase the lap speed one mph at Daytona. For this test the Engine Laboratory prepared three smaller carburetors to reduce the engine power by up to 24%.

The three carburetors were run along with the standard carburetor and give a good picture of the power - lap speed relationship. These four carburetors will be compared on the engine from the car on the dynamometer to give accurate values. Until this data is available we have only the approximate power levels.


Based on these approximations, the car requires 17.5 HP per mph in the 190 mph range. When the correct engine data is available a more detailed analysis will be made.

Correction Factor

It is well known that a great many factors effect the lap speed of a race car at Daytona other than changes in the car itself. Most of these come under the general heading of environmental items: temperature, humidity, barometric pressure, wind and track temperature. For the simpler conditions of drag racing, a satisfactory correction factors was developed for barometer, temperature and humidity several years ago.

For track racing the effects of weather are more complex, and it has been more difficult to develop a successful correction factor. Such a factor has now been developed, and it appears to do a good job of correcting the observed lap speed for temperature and humidity.

It turns out that the barometric pressure is of very small importance, since an increase in barometric pressure increases both engine power and aerodynamic drag by a similar amount. While the basic correction factor equation does allow for barometric pressure, the effects of the range of barometer changes normally experienced is too small to be of any significance.

An example of the usefulness of the correction factor is shown below. The corrected and uncorrected speeds are shown for three different runs with the car in the same condition:

Run DateTimeObserved SpeedCorrected SpeedTemp.HumidityCorrection Factor
611-264:30 PM189.13190.1066°63%1.0050
811-2711:45 AM188.44190.3275°57%1.0100
1011-2712:45 PM188.09190.1878°52%1.0111

In the observed condition, there is a spread of 1.04 mph between these three runs, where the spread is only 0.22 mph for the corrected numbers. These three runs were made before the final baseline was achieved, and are slower than the baseline since the carburetor was not quite reaching WOT [wide open throttle], and there were some air leaks around the front bumper and grille that had not as yet been sealed.

There are other examples during this test of the ability to return to a corrected speed very close to the original under different weather conditions where the observed speeds vary significantly. The corrections are all made to 60°F and 0 humidity.

In checking weather data for Daytona tests and races in the past year, we find that the correction factor was slightly less than 1 for the days before the first day of qualifying in February, 1968. On the qualifying day the correction factor was 1.0044.

This factor corrects Cale Yarborough's pole winning 198.22 mph to 190.05, an increase of .83 mph. Al Unser's qualifying speed of 183.53 mph in car 046 is corrected to 184.34 mph. For the first day of qualifying for the July race the correction factor was 1.0168, so that Charlie Glotzbach's pole winning 185.16 mph is corrected to 188.27 mph, an increase of 3.11 mph. Lee Roy Yarbrough's fastest qualifying time of 187.05 mph is corrected to 190.19 mph. During the various tests run at Daytona during the past year we have seen correction factors between 1.0067 and 1.0183, a difference of 1.2% or about 2.2 mph.

- G.M. Wallace

Chrysler 1904-2018

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