Rex, Woody: chill. IM<HO, this conflict is coming up because everyone is starting to ask the really hard questions about how drag, L/D, inertia, and ballast-based traction all contradict each other in the current designs. Hard questions about previously misunderstood subjects cause strong opinions from smart people. You're both smart enough to understand what really works, the frustration is coming from a limited and partially inaccurate database.
Let's start with Rick's question and A2's comment about ride height vs. drag and design. Any car without a full under tray has tons for stuff hanging out in the breeze for air to hit. This leads to separation and stagnation drag (correctly simplified as "pressure" drag, incorrectly labeled "turbulence") on every single component. One effect of all of the individual components is that the separated boundary layer under the car grows exponentially as the air blows around all of these protuberances. For this reason, many years of Nascar R&D focused on the shape of oil pans with wings on them to act as downforce generators and to smooth things out.
As we lower the car without any other changes, this thick and disturbed boundary layer will tend to choke the flow between it and the ground. This will cause both drag and lift. Where this has already happened, raising the car may decrease drag by reducing the choking effect and giving the air under the car a place to go.
Lower the car/block the front to the limit/skirt the sides: the pressure under the car is reduced, downforce is increased, and very little air from under the car makes it to the back. Why would this be an issue for LSR when it isn't for other racing? In LSR, we need to reduce drag. Without some air to fill in the back of the car, we have base drag: separation.
Now, a clean belly pan is going to have less drag than a bunch of miscellaneous components hanging out in the breeze. So for a conventional car layout, the lowest drag/highest downforce arrangement would be letting a managed amount of air go under the car, skirt the sides, and direct that flow to help fill in the tail separation. The designers of the Gus Gus streamliner have talked about this and how challenging it is.
A clean belly pan with a skirt at the front may generate even more downforce, simply by lowering the nose; i.e. changing to more negative alpha ("rake angle") without raking the chassis itself.
But there are costs: That skirt just stopped any air from going under the car to be used at the back end; more separation, more drag. The air under that smooth pan and behind the blunt nose skirt is fully separated (more drag) and has no energy to be managed for downforce. To get some downforce in a conventional car that air under the car must start out organized, be accelerated to achieve lower pressure (downforce), and stay attached and organized in the pressure recovery area to the tail where it can be directed up instead of just randomly out.
"Increasing downforce without increasing drag" sounds great, and it actually occurs when we start out with a badly separated back end or dirty belly, then clean things up and direct the air properly. If tunnels are used to do this, it appears that tunnels yield downforce and lower drag (for a bad design).
Whether using pencil or CFD, try making sure that every that every square inch of cross section at the back of the car had a source up front and that it's streamline is smooth going around every inch of length, top, bottom, and sides. I'm not going to go into all of the detail theory other than to say, there is no "hole" to close: if the car makes a hole in the first place, go back and start over.
