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Old 03-23-2008, 01:31 PM   #1
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Airdam pictures

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 03-23-2008, 04:02 PM   #2
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Hi Lovemysan,

I think its the belief here and on Ecomodder that the air-dam should not extend lower than any underneath protrusion for best air-drag reduction.

This way the cross-section area is not increased. So, you might take a chunk out of the middle of that air-dam, leaving in the outside portions to direct air around the suspension and tires.

Some grill blocking might be good too. Although, my SL2 would go up over the in-control temp after cruising on the highway while waiting at a long red light on the off-ramp. I would turn on the AC at such times, as it forced the electric fan on. This pulled it right back down in a few minutes.
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Old 03-23-2008, 04:57 PM   #3
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I built my air dam to give about 7 or 7-1/2 inches ground clearance, to match the lowest point of the other hardware under the car. I had a lower one at one point but like yours it scraped pavement far too often. Note that if you put the air dam further back you can have it go down further. As in, if it were even with where the wheels meet pavement, the air dam could be 1/2 inch above the pavement.

Also I built a belly pan that starts at the air dam's bottom edge and goes rearward. I think this is where a lot of the aero benefit is, if there is an aero benefit. Of course the further back you can take your belly pan the better - mine goes approx to the front axles. This spring, hopefully I'll get time to extend it to the car's rear end.
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 03-23-2008, 05:55 PM   #4
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What do you guys think about lowering springs? Seems like that would help, and then you would not need quite the size air dam to have the same effect
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Old 03-23-2008, 07:27 PM   #5
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Some cars benefit from a bit of rake from lowering the front and leaving the stock rear springs. Usually pretty messy ones though.
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I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice
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Old 03-23-2008, 07:37 PM   #6
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Oh, something I'm noticing in airdams that are reported to work well and those that aren't is how far forward they are on the bumper... remember that the air hitting it has to have somewhere to go, if it has a large curvature to travel round to get up over the hood practically reversing direction, then it's probably going to be draggy. Or it has to go quite a long way to spill round the sides, where it might cause extra drag from the wheel wells. Also where it will push more air through the engine compartment as appears to be happening here, will be more draggy.

The front of that Saturn looks rather awkward to work with in this regard. My gut feeling on it, would be to either go the whole hog and drop it straight down from the bumper belt line, with holes cut for adequate cooling, or to go for a shorter deflector that follows the angle off the bottom of the bumper (canted backwards) to push the airflow clear of underbody protrusions, and a short fairing ahead of each wheel.

Planning for winter survivability is a bit of a bugger though, I've been scratching my head somewhat as I look at my vehicles trying to figure how to do something that the snow and icy chunks of slush won't rip off.
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I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice
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Old 03-24-2008, 06:23 AM   #7
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The center was only 1" lower than the main portion of the belly pan. I think I could make a 3" airdam instead and my mileage will be the same and the aircon will work perfect.
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Old 03-24-2008, 05:17 PM   #8
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Hi All,

I vote with Road Warrior. Where the dam is now, its creating a lifting pressure, which causes more drag. This is because of the overhang in front of the dam
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Old 03-26-2008, 11:53 AM   #9
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Been boning up on my aerodynamics lately.... something that might apply to airdams is the leading edge flow separation considerations for an airfoil. A sharper leading edge higher up forces flow separation such that more air goes underneath. This alters the effective angle of attack of the airfoil, tilting back the lift vector. Whereas a drooped and rounded leading edge has a lift vector that is neutral or tilted slightly forwards...

So, if we imagine the car body as an airfoil, by "drooping" the leading edge of the vehicle we force flow separation lower down, such that the lift force vector angles further forward and the induced drag due to the shape of the vehicle should thereby be reduced... this is also the part of the effect resulting when the car is lowered a little at the front wrt to the back.

A sharp angle at the front of the hood on some older vehicles may separate flow there, so grille restriction and nose adaption may have significant effects on those kinds of shapes.
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I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice
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Old 03-28-2008, 09:20 AM   #10
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Quote:
Originally Posted by donee View Post
Where the dam is now, its creating a lifting pressure, which causes more drag. This is because of the overhang in front of the dam
I doubt it is creating lift. My Chrysler has a much longer overhang and I have an airdam that comes down further than that. I removed it once and scared myself on the highway. The additional front end lift *without* the airdam made the steering lighter and it felt like I was driving on ice. I haven't done any testing to prove the extra drag yet, but having the steering feel the same at *edit* high interstate speeds *edit* is worth it.

I vote that the extra drag is caused by the increased frontal area, but I'll bet that the car sticks to the road better like this.
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