....When you size the scoop inlet to CFM with the column of air hypothesis what happens is the engine will reduce the air pressure inside the scoop, you will have a lower air density and you WILL lose HP especially at lower mph! The CFM matches just fine [at the design speed only] but you will have less molecules of air in each cubic foot. If the opening is too big then the engine can't keep up and you get spillage out of the scoop and higher drag. Several other interacting factors come into play! Scoops are Simple - NOT! In some cases the lower HP may have aided traction in the launch but it will cost mph on the far end. Most scoops tend to increase HP some but do you want 50%, 75% or 100% of the potential? 
That's just my three cents! 
Adding to Woody's thoughts I'd personally not size the scoop for an "exact" size CFM wise in high gear. I'd size it for the gear where you are able to run WOT and need maximum HP. For a small motor car the need for a larger scoop opening might be in one of the lower gears where the car is needing to make maximum HP.
In our case so far that situation isn't until we are running our 1 to 1 3rd gear. Even then our scoops have been sized over 10% larger than needed using the CFM required formula that I posted. Still when you look at the scoops we have used they will look quite small compared to what people are use to looking at when watching cars at the drags where they can use HP at much lower speeds.
I also wouldn't size the scoop the same way for one of the mile tracks as you would for the salt as there again you can use the HP in lower gears with the better traction so you don't want to restrict that HP as Woody mentioned.
Size the opening for the first gear where you can use full engine HP with the exception if that is going to hinder drag in the final gear to the point where you would give up some HP at a slower speed to help with drag and the HP needed to overcome it at your terminal speed.
An example of some of this is Speed Demon's inlet opening size...
.... not that large for a car that can make up to 2500 HP, but the car is not to WOT until 380 mph and probably not making maximum HP until past that if at all.
So far here we are talking about the scoop opening only. Once the air gets into the scoop you have another whole bunch of theories coming into play. That is Woody's domain
. Go back and look at the Nish streamliner over the years and you will see a lot of different shaped scoops with very different internal volumes past the inlet. A couple were huge in size past the inlet.
...I need to ask a question.
A turbo charger spinning at full boost will take in a certain amount of air but will a scoop increase that volume?.
What I'm getting at is will more air forced in just stack up at the intake?.
It will stack up if the opening is too large and have to spill around it. You can get a charge effect but I don't think I've ever seen this over 2 lbs.. Still even if it is 1 lb. and you are blown that is just 1 less pound the blower is going to have to make so you will have lower air temps after the compressor which lowers the load on the intercooler.
Sum
