As you might expect, taping up the grille and brake ducts is one of the most effective things you can do when it comes to legally adding downforce. On our ARP-bodied car, taping up the nose was worth over 100 points of front downforce. At 135 mph, that's 100 pounds of extra pressure adding grip to the front tires.
Peltier took things a little farther to see if taping all the body seams to seal them off would further improve the aero. This, as you might expect, had no noticeable effect.
Finally, we experimented to see how a partially taped grille opening affected the car. Adding two strips of tape over the bottom portion of the 28.5x5.75-inch grille added approximately 25 counts of downforce over an untaped grille, while two strips across the top of the opening added approximately 31 counts. This is probably because the tape at the top of the grille created a solid surface for the air to move across that was unbroken all the way to the windshield.
Preston Peltier makes a quick...
Preston Peltier makes a quick ride height check. Because the car's attitude (or the way the body sits) plays such an important role in aerodynamics, it is important to keep track of how every change affects it.
Inspection Height versus Actual Height
It is common knowledge that your race car is rarely at inspection height when it's at speed on the racetrack. Of course, that's fine on the setup plate because you can set such things as camber gain to account for suspension movement. Conversely, testing a car's aerodynamics at ride height or inspection height is a little more problematic. The car's attitude can significantly affect its aerodynamic performance.
If the front end drops because of aerodynamic downforce or simply because the driver applied the brakes, that increases the car's rake, or body height from front to back, which will increase downforce. If the car rolls over on its right side through the turns and lifts the left-front fender, that will allow more air underneath the car, raising the pressure and reducing downforce. Before testing in a wind tunnel, you need to track your car's attitude through a turn and try to mimic that in the tunnel. The easiest way to do this is simply to record your bump stop locations on the shocks after a set of hot laps.
In the wind tunnel, the car needs to be off of its springs and locked at the height you choose. You can do this by fabricating a set of solid struts out of metal tubing that will replace the shocks and springs. If the body moves once the air hits it, it will throw off your findings.
Query and Peltier brought two sets of struts to set the car both at ride height and at the attitude the car will normally be in through the turns. We won't give away those heights because they have worked really hard to develop their shock and spring packages, but we'll say the effect was dramatic. It also changed many of the things we had already tested. As you can imagine, the nose was significantly lower than ride height when the car was set at racing attitude. This not only dropped the front valence closer to the ground, reducing pressure under the car and raising downforce, but it also raised the rear spoiler angle.
If you remember, the spoiler was already reaching stall above 50 degrees on this particular car, so a taller spoiler did no good. Query and Peltier were forced to deviate from the planned test schedule slightly to find the best spoiler angle when the car was raked forward.
Another example is a false radiator box floor the team had tested. The bottom of the radiator box on this car is flush with the bottom of the grille opening. In an effort to build-in a deep gurney lip of sorts (racers may also know it as a belly pan), the team fabricated a piece of sheetmetal that ran from the bottom of the radiator forward to the bottom of the valence. When the car was at ride height, the sheetmetal actually ran downhill from the valence to the radiator. The difference in height was minimal-less than half an inch-but it was enough to hurt downforce. However, when the car was reset at racing attitude, the increased rake indicated that the false floor was closer to the ground at the valence than it was at the radiator, and it helped downforce.