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Old 06-22-2008, 05:54 PM   #1 (permalink)
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95 Chevy Van - remove lower valance?

Hi folks. The lower valance on my full-size van hangs down about 6 inches. Instead of pushing air down, it scoops it up. I have a 2200 mile trip coming up and every bit helps. Do you think if I removed it, my fuel efficiency would improve? There's 16" of space behind the valance (measured to this metal plate under the front axle) if that makes any difference. Advice? The bumper does have some holes I could mount to if I were to home-make something to make the air flow go down and under.

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Old 06-24-2008, 08:09 AM   #2 (permalink)
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Air Dam??

Definition: A front spoiler mounted beneath the bumper and shaped to reduce the airflow under the car. Air dams can increase the airflow to radiators, reduce aerodynamic drag, and/or reduce lift.

The underside of your van isn't very smooth. Less air under there is better.

At first glance, I would say leave the design alone or make it a little bigger..
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Old 06-24-2008, 08:18 AM   #3 (permalink)
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Keep the spoiler, but get rid of those running boards and flares. On 90% of conversion vans I see, the tires are already inside the fender, so all the flares do is increase drag needlessly.
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Old 06-24-2008, 02:46 PM   #4 (permalink)
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The chin spoiler is fine, leave it alone.

What may help would be to temporarily install a rear "box" (top and sides, no back, bottom would be good but optional) to the van. It should extend out from the back of the van as far as you dare (even a foot would help, but the longer, the better). The sides of the box should blend in with the sides of the van just before it curves to the back face, and then taper toward each other slightly (say, 11-12 degrees included angle). The box top should meet the van roof at the forward end, blend with it just before the curve down above the back surface, and tilt downward also at about 12 degrees from the horizontal.

This box would form a type of Kamm-back, a classic low drag design.
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Old 06-25-2008, 05:37 PM   #5 (permalink)
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so all the flares do is increase drag needlessly.

these things surely don't look like they where designed with aero in mind, but fender flares don't always increase drag. especially if there's a large gap between the tire and the fender, as on a lot of older cars (maybe it's got something to do with how the suspention was in those days) anyway, inside the wheelwells there's a low pressure area so unless you want air to be sucked in you'll want to deflect it over the open wheel well, a little agressive flare at the front and the top, might be better than a smooth edge.

of course a fender that hugs the wheel tightly and smooth hubcaps are even better, but it all depends on what's there's and what can be changed.
also wide fenders at the back might make wheel skirts much easyer and cleaner to do.


as far as the airdam goes ,get on you knees and look underneath the van to see what the airdam shields, if there's plenty of stuff visible below the dam, you might want to extend it, it doesn't have to be straight, the sides can be lower as they'll shield part of the tire and the suspention. since it's metal i'll have to much ground clearance to prevent damage anyway.

also gigen the size and shape of the radiator some sort of grillbock, maybe one wich can (partly open) could work wonders for your FE

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