[slowbird]

Anyone have any idea how the aerodynamics of running a car without a hood effects the performance? I would think that there would be a little mph lost without a hood (maybe .5mph) but not really sure. Just wondering what you guys think.

[Tom Vaught]

Originally Posted by slowbird

Anyone have any idea how the aerodynamics of running a car without a hood effects the performance? I would think that there would be a little mph lost without a hood (maybe .5mph) but not really sure. Just wondering what you guys think.

This is the way i think the air will go based on spending time in the Lockheed Wind Tunnel at different times over 10 years.

1) The air will meet the body/ bumper with some of the air going upward over the grill and some passing downward under the bumper. Any air under the vehicle is banging into stuff: Suspension parts, tires, rear axle, exhaust, etc. (slowing the vehicle down).

2) Normally A vehicle with a hood will have the air going under the vehicle which will produce a low pressure area as the air tries to get out from underneath the car. How much air passing under the vehicle is a function of the vehicle height and any "spoiler" strategy under the bumper. Normally, Air from the grill/radiator moves to the rear of the engine compartment, runs into the firewall, and exits under the vehicle. Manufacturers try and limit the amount of air passing under the vehicle. The 70s Trans Ams used Air extractors on the sides of the fenders to help relieve the pressure/ volume of the air trapped in the engine compartment vs exiting under the car. IT worked!

3) Vehicles with "cowl hoods" not connected to the engine have some of the air banging off the firewall, out the hood, and travel over the windshield.

4) In your case the air will hit the grill and bumper, bang off of whatever is in the engine compartment, bang into the firewall, and then exit either under the vehicle or over the roof. Virtually no aero effect as far as smoothing out the air traveling over the vehicle. Might as well have an open front end Roadster.

5) Cooling on vehicles driven on the street typically suffers, depending on the engine.

Conclusion: You will have a lot of "DIRTY AIR" around the vehicle.

6) The aero works as speed squared. or said another way:

Wikipedia: http://en.wikipedia.org/wiki/Drag_%28physics%29

"With a doubling of speed the drag (force) quadruples per the formula. Exerting four times the force over a fixed distance produces four times as much work. At twice the speed the work (resulting in displacement over a fixed distance) is done twice as fast. Since power is the rate of doing work, four times the work done in half the time requires eight times the power."

So you screw up the aero designed in the vehicle I really doubt if the effect would only be 1/2 mph at the end of the run. JMO

Tom Vaught

ps Travis and Rodney did a nice job on changing the AERO of the 63 Tempest on their new race car. Freed up some extra power for them.

[Steve C.]

Curious, and sort of related. We have seen cars that have flat hoods with a tall intake manifold/air cleaner set up high enough so that the air filter is sticking out above the hood thru a hole and subject to impact from the car moving forward. Going town the track at speed is there any detremental effects on the ability for the round air filter to draw in air with air flowing around it ?

[Gach]

Tom...I remember seeing Marty Palbinkin 70 GTO, he was running a spoiler on the front under the bumper, dose that help ( stop ) air going under the car, and do you know ( have idea ) how it effects air going into the engine compartment. Also any ideas or information on forward facing air scoops.

[79TA455STROKED]

my buddy with a 72 split bumper camaro lost his unpinned hood during a run at track.Rest of the day with no hood,he was down 3mph!!!!!
This was a 150+mph smallblock,procharged car.

[lust4speed]

Regardless, it is best to make the choice on hood or no-hood before staging. Nick Anderson went the last 300 feet without the hood at 2007 Pontiac Heaven. No data is available whether his MPH changed. The hood did prove to be somewhat aerodynamic and sailed down just missing the track photographer.

[Tom Vaught]

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$$$$$$$

(:>(

We did Marty's Car to try and keep the air out from under it for sure. We also had some clear plexiglas pieces to keep some of the air out of the wheel wells at Norwalk that first year. The Track Announcer gave the car a lot of Chit with the spoiler, plastic pieces, rear wing, etc UNTIL MARTY RAN FASTER THAN ANYONE IN HISTORY WITH A PONTIAC 400 BASED ENGINE AND SOME CAST IRON #62 HEADS. LOL!

Marty P. undersood Aerodynamic concepts due to his job as a Hawker Pilot for a large corporation.

Travis and Rodney, like i said, have gotten a good handle on their car too. Travis and I talked about the deal several times over the years.

The aero stuff makes a lot more sense when you are really going fast.

Tom Vaught

[Gach]

UNTIL MARTY RAN FASTER THAN ANYONE IN HISTORY WITH A PONTIAC 400 BASED ENGINE AND SOME CAST IRON #62 HEADS. LOL!

I remember that very clearly...because I got a call from Bob Maxey...he said someone just ran ( if I remember coreectly ) a 7.40 with a 70 GTO at Norwalk.
Bob was blown away.

Marty is a supper nice guy, talked to him many times. I met him at Maple Grove..I bought the E-heads off the car he had at Maple Grove.

[Tom Vaught]

I miss Bob Maxey, A LOT, He was very close to Mike V from Canada. He died too soon.

Yep, 7.40s at 194 I believe was the best of the days runs. This was when everyone else was breaking into the high 8s.

Tom Vaught

[Gach]

I miss Bob every day, the one guy you could get real answers from. Real old school where your word meant every thing. I mention I need a Turbo 400, he said I got one I'll sell you, it was the spare out of his Grand Am ( still in my car to this day ) I asked him how much, he gave me a price...I said ok...when I get the money I'll get it. So save it for me, do you want a deposit....nope.

A week later the trans showed up at my house, I was real nevious..so I called Bob and said maybe you miss under stood me, I don't have the money right now, he said well give it to me when you got it, I said well I don't like doing that only because I don't know when I'll have the money, he said well has your word changed in the last 8 years I've known you. We talked at least 2-3 times a week, 6 months later I paid him for the trans...he never once ask me about the money in that whole six months.

After he die...Mike V..spent days helping his wife. sell all of Bob's stuff he had tons
of stuff.

[slowbird]

I figured that there had to be something there. At least I know there is more there once I get the hood on.