Blue,
I agree about having all the air go around if possible, but in my scenerio, I am not concerned with B-Ville rules and the vehicle will have a grill, and radiator opening and a radiator. No LSR car with a water tank and sealed nose.
I am talking about a vehicle (street driven, not just legal) that will be ran at the Texas Mile and the USFRA 130 or 150 MPH club, after being driven there.
I am talking about a truck, not an aerodynamic sports car. I know that air gets pressurized under the hood IF there is no place for it to go. Unfortunately, most of the time the best place for it to escape it around the engine and out the bottom.
I do know that Smokey Yunick did extensive testing with airflow ducting 50's, 60's and 70's with slab nosed Chevys. He proved mph would go up by releasing the underhood air, but the actual methodology he used is rather vague and from what I can tell, something he took to the grave. I have most of his books and while he talks alot about it, he elaborates on his methods little. I am sure that was to keep a competitive edge. In one example he gives, in many different books, he was sitting on the floor of a 55-57 Chevy and they where doing 120 mph, he unscrewed the heater block off plate from the firewall and the air flow blew him back, while the car gained 20 mph.
I posted it here, because frankly, when it comes to airflow, the members on most automotive bulletin boards are lost in the woods. I know more than most of them just from my helicopter maintenance background.
Perhaps the best thing for me to do is rig up a manifold with various ports on the firewall, tie it all to a psi gauge and drive at various speeds. Then I can extrapolate some sort of data.
If you check my site listed in my sig, you will see the truck I am modifying to be a rolling test bed of ideas, while we gather parts for the V4F/MGR
C. J. Daniel