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Old 05-13-2011, 01:10 AM   #1 (permalink)
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belly pan vs air dam

i searched and searched but couldn't find a proper answer on this

anyways, my first thread here, i have a 99 dodge neon

- what would have a better impact on FE (assuming a grill block and other basic arrow mods are allready done)

a 4 inch lawn edging style air dam like many threads have shown,

or

doing a proper underbelly pan, basically covering everything but the exhaust

but

both is obviously a great answer but will you loose all effects of the belly pan with an air dam?

thanks
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Old 05-13-2011, 04:21 AM   #2 (permalink)
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Quote:
Originally Posted by moparrr07 View Post
both is obviously a great answer but will you loose all effects of the belly pan with an air dam?
You won't.
Even with an air dam, there's a lot of air going underneath the car , and it's still going to interact with and cause drag on the belly of the car.

If you run an air dam down to the level where you could fit a belly pan, that would be close to optimal.
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Old 05-13-2011, 10:31 AM   #3 (permalink)
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I've been wondering the same thing.

My (rudimentary) understanding is that the airdam helps by directing the air away from the underside of the vehicle where there's lots of junk to cause drag. The airdam would increase the frontal area (I'm sorry if I'm misusing the term - please correct me if I'm wrong) but the cost here is supposed to be more than made up by the reduction in drag from under the vehicle. But if you do a proper belly pan, will the airdam still be a worthwhile investment or will the increased drag of the airdam negate or maybe even exceed its positive impact?

It would seem to me that the use of both a belly pan and an airdam might well produce low pressure area under the vehicle that would increase downforce (and probably improve handling) but might also increase drag?
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Old 05-13-2011, 11:35 AM   #4 (permalink)
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...it's a trading-point issue: (1) airdam trades "directing air AROUND" the car for slightly increased total cross-sectional area, but it's a net GAIN in the end. (2) belly pan provides LESS air-turbulence creating nooks & crannies to under car air flow that gets past/under the airdam.
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Old 05-13-2011, 02:18 PM   #5 (permalink)
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dam/belly

Quote:
Originally Posted by pnambic View Post
I've been wondering the same thing.

My (rudimentary) understanding is that the airdam helps by directing the air away from the underside of the vehicle where there's lots of junk to cause drag. The airdam would increase the frontal area (I'm sorry if I'm misusing the term - please correct me if I'm wrong) but the cost here is supposed to be more than made up by the reduction in drag from under the vehicle. But if you do a proper belly pan, will the airdam still be a worthwhile investment or will the increased drag of the airdam negate or maybe even exceed its positive impact?

It would seem to me that the use of both a belly pan and an airdam might well produce low pressure area under the vehicle that would increase downforce (and probably improve handling) but might also increase drag?
with two of my vehicles I saw an improvement when the airdam was lowered in front of a full bellypan.
I've never gone lower than the bottom of the lowest suspension member,but it is lower than what the SAE recommends for clearance for driveway ramps,etc..
And clearance is limited such that I must be very diligent when approaching curbs,even with a flexible lip down there,or it's 'whammo'!
Ford chose an active front airdam for its PROBE-IV concept car which had a really nice bellypan.That car also had active suspension which would alter ground clearance ,plus angle-of-attack as a function of driving speed.
Volvo has also produced a speed-sensitive active front dam.
Many current supercars employ active suspension and active rear spoilers for high speed stability and safety,but not so much in the way of active front dams.
You are correct,that when lowering the dam you'll finally reach a point where the frontal area will begin to be aggravated.And at some point,the drag reduction will overshadow the increase in CdA.Then drag will rise again,canceling the gain.
Only testing will determine the cross-over point.
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Old 05-13-2011, 02:25 PM   #6 (permalink)
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Quote:
Originally Posted by pnambic View Post
My (rudimentary) understanding is that the airdam helps by directing the air away from the underside of the vehicle where there's lots of junk to cause drag. The airdam would increase the frontal area (I'm sorry if I'm misusing the term - please correct me if I'm wrong) but the cost here is supposed to be more than made up by the reduction in drag from under the vehicle.
You're right there.

Quote:
But if you do a proper belly pan, will the airdam still be a worthwhile investment or will the increased drag of the airdam negate or maybe even exceed its positive impact?
The belly pan will likely be lower than the current lowest point on the front bumper.
You don't want to make a scoop by angling the front belly pan up, that'd scoop more air underneath the car.
Instead, you can direct that air sideways by fitting an air dam that's as deep as where your belly pan is.
That way, you also don't increase the frontal area beyond what you get anyway with the belly pan mounted.


Like aerohead says, you could see further gains by extending the airdam even lower, but there you're in the trade-off area - increased frontal area against the benefit the airdam gives you.
It could work for you, or it could work against you, depending on the car.

Once you have a belly pan you can start experimenting with different airdam depths and see what works best.
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Old 05-14-2011, 10:16 AM   #7 (permalink)
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I added an air dam to my VW diesel. My mileage has dropped a mpg over two tanks. I blame the increased frontal area. I am taking it back off.

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Old 05-23-2011, 02:58 PM   #8 (permalink)
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Varn extinguished an idea i had as i was reading this. My thought was to make a very low air dam on a hinge with a trunk lift shock or two. That way it would be dropped as low as possible for driving. It could scrape and move out of the way over speed bumps but then not do any damage to the unit. Then the shock(s) would push it back into place.

But if it makes too much frontal area to be effective then that ones out the window. Though I seem to recall a Dodge Ram with a huge air dam. Dont know if it worked out for him though.
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Old 05-23-2011, 05:03 PM   #9 (permalink)
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Quote:
I added an air dam to my VW diesel. My mileage has dropped a mpg over two tanks. I blame the increased frontal area. I am taking it back off.
most air dams that go all the way down like on nascar racers allow the air to escape over the car, but on this setup it seems like the air can only go round the car, and that's gonna add to the wake at the sides. (the front tires add a lot of turbulent flow, so this path is likely aerodynamically even less favorable than the underside)

what you want is full height dams in front of the tires but a raised dam in the center, sending a little air under the car that would otherwise have to take a route of even more resistance.
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Old 05-23-2011, 05:11 PM   #10 (permalink)
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Hi Ford,
Don't take my word on it. Your vehicle may be different than mine. Air can behave unpredictably when you attempt modifications at home. Others have had good luck with it. Keep trying.

I feel that I must be getting fairly good air flow under the car rather than having it go over the top and around the side. the nose of the car is exceptionally blunt.


Quote:
Originally Posted by Floordford View Post
Varn extinguished an idea i had as i was reading this. My thought was to make a very low air dam on a hinge with a trunk lift shock or two. That way it would be dropped as low as possible for driving. It could scrape and move out of the way over speed bumps but then not do any damage to the unit. Then the shock(s) would push it back into place.

But if it makes too much frontal area to be effective then that ones out the window. Though I seem to recall a Dodge Ram with a huge air dam. Dont know if it worked out for him though.

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