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Old 04-03-2008, 11:43 PM   #1 (permalink)
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The airdam that didn't work

Last august I made a trip to georgia. Before I left I fabbed up this airdam. It gave 5.5" of ground clearance. It was made from 26 gauge HVAC sheet metal. The first 3 hours of the trip netted excellent results(tailwind). Upon turning south mileage plummeted. I put 750miles on it with worse than usual mileage. I did some early morning 60-30mph coast down test. The results were very close but the without the airdam I got a very light improvement. This confirmed my suspicions that it was indeed hurting performance. The airdam certainly had its advantages, the A/C worked as good as stock at highway speeds. The added high pressure on the cars nose made for excellent cooling properties(Which was nice for a trip to Georgia in august). It also just looked cool. I couldn't have gotten more looks if I was driving a hot pink pantera. It was however impossible to live with. Even the most gently graded driveway would defeat it. Gravel is the enemy of any airdam. It wouldn't last 20 minutes on an icy winter day. The presence of mind required to prevent its destruction was mentally draining. I think for proper performance in my case the airdam and belly pan must be integrated together.




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Old 04-03-2008, 11:59 PM   #2 (permalink)
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Did you have the full bellypan before or after the airdam?

I've had excellent results with my airdam, though without a bellypan.

I have since taken about 4" off my airdam (essentially making it a grille block) and added front and rear undertrays. I haven't had a full tank of gas through it since, but I'm interested to see the results.
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Old 04-04-2008, 02:37 AM   #3 (permalink)
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lovemysan, you should enter your car in the EM Garage so that we can learn from your experience. I just entered mine.
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Old 04-04-2008, 09:21 AM   #4 (permalink)
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That was nice looking. I had a similar experience with airdams. I started quite radical with a 7" airdam. It looked interesting but rubbed alote (luckily it was made from coroplast so it held up well) and coast down tests showed a slight decrease in performance. I ended up shaving it so it was 3.5 - 4 inches tall (just enough to block most of the undercarriage components from the air flow). It looks okay, doesn't rub anymore, and the coast down test were inconclusive (showed no decrease in performance over no airdam) so I just left it on. I'm not using any kind of belly pan in the front of my car though. I may try a belly pan vs airdam once temps stay warm.
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Old 04-04-2008, 12:44 PM   #5 (permalink)
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airdam (damn!)

Great photos,and love the look of your work! I think your project fell victim to the diminishing-return/negative-return,as the depth of the airdam added a significant increase to the cars frontal area,increasing drag by a corresponding factor.Should you have had Hucho's book,you would have found that if the airdam projects below the elevation of the lowest suspension member,drag will begin to grow as a percentage of the percentage increase in frontal area.Bummer! The book is invaluable to any one considering aero modifications and can soon pay for itself in time and material saved.
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Old 04-04-2008, 02:05 PM   #6 (permalink)
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The air dam was 1" lower than the center section of the pan. The pan actually actually declines from the bumper to suspension 3-4". Also the airdam was not level with the ground it was 5.5" in the center and roughly3.5" on the outside. I'd like to get that book but don't have $40 to spend on it. I need new motor mounts.
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Old 04-04-2008, 09:11 PM   #7 (permalink)
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What's behind the lower lip of that spoiler? Does it just hang down, or is there a tangential horizontal surface that is part of the undertray? Could make a big difference.
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Old 04-04-2008, 09:50 PM   #8 (permalink)
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"Even the most gently graded driveway would defeat it."

I used to drive a tow truck and we had the same problem but for a different reason. If you drive up a steep grade in a tow truck while towing a car, the back of the tow truck drops and there is a risk that the car on the back will hit the road and fall off. (don't ask me how I know this) The solution is to approach any grade on an angle. Now for a speed bump this would be difficult, but where you are going into a parking lot that has a steep grade, try to go in at an angle, so only one wheel hits first.

I hope that makes sense?

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Old 04-05-2008, 01:14 AM   #9 (permalink)
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Heynow999 offers a good suggestion. I always see lowered cars take speed bumps and driveways at an angle. Speed bumps are handled with a zigzag pattern...moving to the leftmost area of the lane, cutting sharply to the right across the bump, and straightening out in the rightmost area of the lane.

I'd lose the antenna. I'd bet you'd decrease air drag a healthy fraction of a percent.

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Old 04-05-2008, 07:10 PM   #10 (permalink)
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Quote:
Originally Posted by lovemysan View Post
Last august I made a trip to georgia. Before I left I fabbed up this airdam. It gave 5.5" of ground clearance. It was made from 26 gauge HVAC sheet metal. The first 3 hours of the trip netted excellent results(tailwind). Upon turning south mileage plummeted. I put 750miles on it with worse than usual mileage. I did some early morning 60-30mph coast down test. The results were very close but the without the airdam I got a very light improvement. This confirmed my suspicions that it was indeed hurting performance. The airdam certainly had its advantages, the A/C worked as good as stock at highway speeds. The added high pressure on the cars nose made for excellent cooling properties(Which was nice for a trip to Georgia in august). It also just looked cool. I couldn't have gotten more looks if I was driving a hot pink pantera. It was however impossible to live with. Even the most gently graded driveway would defeat it. Gravel is the enemy of any airdam. It wouldn't last 20 minutes on an icy winter day. The presence of mind required to prevent its destruction was mentally draining. I think for proper performance in my case the airdam and belly pan must be integrated together.
I am not surprised from your results.
with your airdam, you have added more frontal area, and because your car (with many aero mods) it is very efficient, your have gotten worse the things.
If I just remember, your car is equipped with full bellypan.
You can try to reduce central height of airdam, this, reduce the FA, and permit to pass the air under your car.
Look, the example opel calibra.
Calibra equiped with engine undercover, use an airdam tested in windtunnel.
After many tests, Opel are deliveryd an airdam shaped with raised central area, and high at the side.

look the image below:



It permit to deviate the air from wheels and the suspension arm.
I do not have any report, but in my car, I am insirated me to Opel for my front deviator
if you try it, tell us the change.

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