How do you INCREASE downforce and REDUCE drag.[/b]
It's not as difficult as you think. First, some basics:

- Lift causes drag. Pilots and aeronerds know that you cannot increase lift with a wing (or any surface, really) without also increasing induced drag (the drag produced not by the resistance to airflow - parasitic drag - but that created by the force of lift itself).

- "Downforce" is a bastardized simpleton NASCAR term; for the most part, very few cars produce "downforce" without wings or special underbody tricks. In fact, NASCAR has done a whole lotta stuff to these things to KEEP them from "producing downforce". In the real world, of which NASCAR is a part, the best you can do for a wingless, undertray-less automobile is MINIMIZE LIFT.

- Airflow beneath a car - without special undertrays - is turbulent, thus creates drag. (That's why you see The Boys faring in exhaust system and crossmembers and such. How many of you are paying attention to such details when building your exhaust...?)

- Airflow beneath a car - absent special undertrays - creates lift due to Bernoulli's Equation.

- Airflow through a cooling system is EXTREMELY draggy, not only because it is extracting copious energy from the cooling system but its passage is horribly turbulent. You'd be amazed at the total drag on most cars simply from the cooling system. ('Tis why manufacturers love small grills.)

Ergo, what is actually happening by taping up the "radiator" for a short while is that airflow through the cooling system is being reduced and airflow beneath the car is being reduced. This is not CREATING DOWNFORCE (thus creating drag) it is actually REDUCING LIFT (reducing drag). Reduced lift = reduced drag; reduced turbulent airflow = reduced drag. Reduced drag = Old Ford Falcons with pretty bodywork and decals go faster.

Quite simple, really...


...in drag "racing" they prefer lower elevations....why if higher elevation was less dense air?[/b]
Lower elevation = more dense air; more dense air = more oxygen molecules per cubic inch of air. More of that means bigger "go boom".

The power increase from the increased oxygen in denser air far exceeds the increased drag from it; to a point. For example, if I am williing to let the engine in my light airplane rev to whatever it wants, I can exceed the redline at sea level and make some serious speed from the inreased power. However, if I limit my flying to redline my best speed at attained at around 8,000 feet with full throttle (less intake restriction) due to the reduced drag. Any lower and I have to pull back on the throttle to stay within redline; any higher and I cannot make enough power to reach redline.

A turbocharged or turbine airplane, on the other hand, can fly much higher and will make better speed up high because it will hav ethe decrease drag from less denser air PLUS increased power from turbocharged manifold pressure. That's why commercial aircraft, almost all powered by turbine engines, fly as high as possible.

...why are lap times on cool days sometimes FASTER?[/b]
More oxygen = more power. More power = faster lap times.