As stated above, the air flows from higher pressure to lower pressure. The air dams create a pressure differential by keeping the air in front of them, and not allowing it to go under the car at the core support. The air goes to the path of least resistance, which is through the radiator. There is a seal along the top of the core support that also precludes the air from going over the core support. There are also vertical panels at both sides of the core support, and attached to the bumper support, directing the air toward the radiator. The OCC bumper cover has a hole in it to compensate for the solid center of the grille blocking frontal air flow.
You may be hurting yourself with the placement of the intercooler. The flow coming in the grille may have more pressure than the air coming from the hole you are proposing, and consequently get back flow through the intercooler. Since you want all of the radiators to work efficiently, you may need a larger engine cooling radiator, and possibly a larger AC condenser, or some pretty hefty fans. You also have to contend with the cross braces on the core support. The engine makes most of the heat you need to get rid of, and you do not want the intercooler to get hot air at all. if the intercooler only covers part of the radiator, that is allowable. You can even put a push fan on the intercooler to get a little more air through the whole system. Adding a hole in the bumper is not a bad idea, but only if you move more air through the radiators. If you do not, the air dams will be less efficient, because you are creating more pressure above them, and it will try to push the air in front of the air dam back down, instead of going up and through the radiator. You could put extensions of the side air direction panels to the bottom of the center air dam, but they may cause more trouble than they are worth by interfering with parking, and going over bumps in the road.
A lot of race cars use a "splitter" at the front to keep more air out from under the car. The more air you keep out from under the car the less lift you will have. You can interpret that as down force, but it does not increase the down force, it only removes lift.
Years ago, there was a car called the Chaparral. The last version had a small auxillary engine in the rear that ran a pair of fans to vacuum the air from under the car. It was outlawed at some point because it was extremely fast, and was too far ahead of the rest of the other car's technology. If the vacuum engine quit, the car did not handle nearly as well. They also had Plexiglass side air dams along the entire side of the body with slotted holes to allow them to move up and down with the road, and wear. Today a lot of sports cars use tunnels that exit at the rear to use the vacuum created by the car going through the air to extract air from under the car.
Putting a flat pan under the car, with the exception of the exhaust system, and smooth the airflow under the car as much as possible, can thereby decrease lift.
No matter what, you must balance the "weight" on the car to keep both the front, and rear tires on the ground. Back in the late 60s and early 70s, Ford put a spoiler on the Mustang. It was pointed up just a little at the front. It caused the rear to lift, and position the body to obtain more down force on both the front and rear. Some ingenious fool decided that he knew more than Ford, and decided to tilt the spoiler down in the front. He found out that it did put more down force on the rear wheels, but the front wheels would lift off of the ground at high speeds.
No matter where the air flow is coming from or going to, the smoother the path, the more flow you are going to get.
1991 OCC 461 (.030 over 454) BBC, 3.23 posi, flash to pass, drop spindles & springs, Impala rims, Hydroboost, Recaros, MOMO/wood SW w/QR, custom wood shift knob, Pioneer DEH P77DH
1992 OCC now with 5.7 tbi, DEH P77DH
For a parts list, check https://www.impalassforum.com/vBulle...ion-parts.html
Last edited by Fred Kiehl; 08-17-2019 at 09:40 PM.