[beetle1303]

Hey Panel,
first of all you have a relly hard *** kicking bus. Its absolutely awesome.
I agree with everybody that said "go under". The reason is one and simple.
The bus doesnt have any aerodynamics (unfortunately), still great though, it is the same a solid brick (going plain to make my self clear.no offense). when air is blowing from one side, because of the graet frontal area the air pressure increases significantly (that why when pop you pop outs it should be realy breazy specialy when speed increases).But what happends from the edge of the brick's frontal area and backwards? Again a simple answer. Now think of a cut away of a tube. The more you bend it the more turbulent flow you get. This happens because the molecules of the medium running in the pipe (liquid or gas) that are towards the inside of the "turn" will try to continue moving straight thus creating a turbulence to the flow.

for the same reasons your roof scoop cant provide the "calculated air flow" or air supply. same with the nacas. In order to achieve their max performance you will need really big ugly and actually silly scoops to direct air into them.

A VERY IMPORTANT THING The longer the pipe the lowest the pressure you get at the end (for gases with ambient air flow)
Something on the above. A friend of mine has a beetle only for tarmac hiil-climbing or circuit racing. he runs a 2.0L type 1 with the normal style fanshroud and in order to provide enough air he uses a twin naca you were saying on each quarter window with 12x12 cm lexan "eyebrows" with a massive 8 cm opening. The car will ran at acceptable to high temps through the championship, but when its raced when really hot about 38-43 degrees C it suffers. The car is still able to wipe out any car in the competition.

Anyway
I hope that some of these will help. I know its long, but i believe it gets into things a bit more.

Chris.