Aerodynamics / air dam / cooling - Chevy Impala SS Forum
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post #1 of 48 (permalink) Old 08-16-2019, 09:00 PM Thread Starter
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Aerodynamics / air dam / cooling

One area I am admittedly deficient in is my knowledge of automotive aerodynamics. Im working on the heat exchanger setup for my LSA build and I had to really put some thought into the packaging of it so not to hinder flow too much to the radiator/ac condenser stack or trans cooler.

My best option was to place a large 38x9 HX behind the front bumper support, probably welding up my own tubular support and then cutting out a rectangle in the bumper so air can pass straight through. This keeps a good section of the radiator stack up behind the grille unobstructed but should give free air flow into the HX.

My only concern now is aerodynamics. After all, with 700rwhp this car will be seeing much higher speeds on a 1/2 mile track or even 1/4 mile track than a stock SS.


Ive heard the air dam helped to force air into the grille. How does it do this? How does it affect downforce and what implications might a big old cutout in the bumper have on all of this?

Input welcome, and id love to hear from anyone who has some knowledge in aerodynamics

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post #2 of 48 (permalink) Old 08-16-2019, 09:07 PM Thread Starter
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Pic for attention lol
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96 BBB Pro Touring- In the works- Mods list includes functional money incinerator, should have stuck to bolt-ons button, 100 dollars in mild steel MIG wire, a really expensive air compressor and a letter from Tire Rack saying nobody makes 335/35/17's anymore. (396/AI heads/D1SC)
https://www.impalassforum.com/vBullet...formance+build --frame off build up thread
Old N/A setup http://www.youtube.com/watch?v=3ZvPZi9fL8k 396, LE2 heads, TH400
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post #3 of 48 (permalink) Old 08-17-2019, 11:55 AM
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Quote:
Ive heard the air dam helped to force air into the grille. How does it do this? How does it affect downforce and what implications might a big old cutout in the bumper have on all of this?
For the how and why you might poke around some NASCAR sites. The FSM is clear that the car needs the factory parts to cool. I would expect what you are suggesting will affect things but GM did do the bumper cutout on the Olds Custom Cruiser Wagon Bumper. I can not prove it but the air from the air dam seems to be more important at highway speed and the grill more important in city traffic. Removing the lowest parts seems to allow the fans to pull air from under the car back through the radiator resulting in higher temperatures.



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post #4 of 48 (permalink) Old 08-17-2019, 03:37 PM
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Airdams create low pressure area(s) behind radiator that encourage more air flow form above,and below...

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post #5 of 48 (permalink) Old 08-17-2019, 09:36 PM
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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.

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Last edited by Fred Kiehl; 08-17-2019 at 09:40 PM.
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post #6 of 48 (permalink) Old 08-19-2019, 01:22 PM
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"but the front wheels would lift off of the ground at high speeds."

🙄🙄

Look at just about any photo of 69 or 70 mustangs in TA competition back then.
They ran that wing because that was all that was homoligated (sp).
Now look at the angle they ran at trying to get it to do anything.

As for front wheels coming off the ground, sit two 200 lb guys on the trunk of a mustang where that wing was mounted.
Front wheels ain't coming off the ground!
You might cave the trunk in though.


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post #7 of 48 (permalink) Old 08-19-2019, 01:28 PM
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Front splitters are not just about keeping air out from under the car, but managing it.

Remember the old blow between 2 pieces of paper deal.
Same car different splitters ,camaro
Edit 3rd pic is bentley
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The First
LS7 T56 6 Speed Wagon
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LS7 T56 drag video
My Wagon
My W-31 Cutlass

Last edited by 95wagon; 08-19-2019 at 01:45 PM.
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post #8 of 48 (permalink) Old 08-19-2019, 01:31 PM
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Real rear wings! Some of the stuff in the shop
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post #9 of 48 (permalink) Old 08-19-2019, 01:34 PM
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Continued
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post #10 of 48 (permalink) Old 08-19-2019, 01:44 PM
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