aerodynamicsaircraftlift
I've read many times, including here on this very site that the commonly known explanation of flight is wrong, and that airplanes can fly because the shape of their wings deflects air down. This makes sense, but as far as I can tell it doesn't explain upside down flight or symmetric wings.
The images I've seen show an inclined wing, which forces the air to go downwards. But how can planes fly upside down then?
A short summary of the paper mentioned in another answer and another good site.
Basically planes fly because they push enough air downwards and receive an upwards lift thanks to Newton's third law.
They do so in a variety of manners, but the most significant contributions are:
Explanations showing a wing profile without an angle of attack are incorrect. Airplane wings are attached at an angle so they push the air down, and the airfoil shape lets them do so efficiently and in a stable configuration.
This incidence means that even when the airplane is at zero degrees, the wing is still at the 5 or 10 degree angle.
-- What is the most common degree for the angle of attack in 747's, 757's, and 767's
Any object with an angle of attack in a moving fluid, such as a flat plate, a building, or the deck of a bridge, will generate an aerodynamic force (called lift) perpendicular to the flow. Airfoils are more efficient lifting shapes, able to generate more lift (up to a point), and to generate lift with less drag.
--Airfoil
The problem you've formulated is that these two cars are identical aside from the mass difference, so let's just limit this to two identical cars where one has an added weight in it. The heavier car will accelerate slower, based on simple $F=ma$, where $F$ is the same, so $a$ must be smaller for a larger $m$. Friction, which determines the max speed along with the force, is a little bit messier.
The air resistance is basically only affected by the shape of the car, so it will be completely unchanged. The heavier car, however, will have greater ground friction from the contact between the wheels and road and because of that will have a slower max speed. One way you can convince yourself that the tire friction depends on the weight of the car is to just consider that the the tire deforms and creates heat, and greater mass will cause it to deform more every turn. For super fast cars tire friction is actually extremely significant.
Due to increased formalism by the question, I can offer a little more detail. Here is a really basic force diagram I made for this. It's not perfect, but I think it's sufficient. And by the logic of the question, $F_{drag}$ is broken up into 2 parts where one is from the body and one is from the wing. Furthermore, the wing aerodynamic forces are really the wind specific drag plus $F_{wing}$.
So, we were talking about increasing the weight of the car. That increases $F_g$ and $F_{ground}$ because in real life the wheel friction force has a significant dependence on the weight. The question mentioned the need for the wing in order to maintain traction. So, traction is a tricky point, because it is related to the weight.
$$F_g=M g$$ $$traction = \frac{M g+F_{wing}}{M g}$$
It is my belief that if a given turning radius without slipping was needed for a race car, this quantity is what would need to be kept constant. I think this gets to a little of what the question wanted, which is that if the mass, $M$, changed, some redesign would be necessary to maintain the same traction (see the above equation).
Best Answer
Upside-down or right side up, flight works the same way. As you stated, the wing deflects air downward. When inverted, the pilot simply controls the the pitch of the aircraft to keep the nose up, thus giving the wings sufficient angle of attack to deflect air downwards.
Most airplanes are designed with some positive angle of attack "built-in," meaning that there is some angle between the wings and the fuselage so that the wings have a small positive angle of attack while the fuselage is level. This is why the floor isn't tilted tailwards when you're in an airliner in level flight. So when upside down the nose has to be held a bit higher than usual, and the other flight systems (including the pilot!) must be designed to handle it, but there is nothing really special about upside-down flight.