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Old 05-07-2020, 11:49 AM   #11 (permalink)
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Quote:
Originally Posted by JulianEdgar View Post
Yes, I'd be very surprised. The only car I know of like that is the first Chevrolet Volt, and if you read the SAE tech paper, you can see why it ended up like that. Have you got some pics of cars running standard air dams and smooth undertrays?
Quote:
Originally Posted by California98Civic View Post
That's very interesting. Why do you think so many have both undertrays and airdams? I would love to see more of the photos. I have long needed to do more under the car, but I dislike the extra access difficulties an undertray creates.
Here are a few examples off the top of my head. Of course, the aforementioned Volt:



Also its sibling, the now-departed Malibu:



(Sorry, some of these pictures I was more interested in the wheel strakes than the air dam).

The Audi A4 uses a sectioned air dam and undertray:



So does the TT:



The Honda Clarity has this curious center air dam despite an almost completely-covered underside:



The Kia Telluride uses a full air dam, separate wheel strakes, and engine undertray:



And of course, the Mustang Ecoboost has this interesting air dam + undertray combination (this one isn't my picture):



I can't speak to why these designs are out there. Your guess is as good as mine, which is pretty worthless without any data.

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Old 05-07-2020, 11:49 AM   #12 (permalink)
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Might be a little better if we had pics from you own car. Personally, I am not sure flush with the front in best. Mine is set back a little like some of the others, like this:

Julian is right that there are other improvements to make here, but that airdam is really well placed, and importantly, the further forward you place it, the more it will scrape ditches and bumps, the more it will beat into parking stops. Mine works great. I once diagnosed it must have broken loose and sagging by a drop in freeway MPG. I pulled over to check... and there it was... resecured it... MPG returned. For me it makes a big difference.
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Old 05-07-2020, 06:21 PM   #13 (permalink)
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Quote:
Originally Posted by California98Civic View Post
Might be a little better if we had pics from you own car. Personally, I am not sure flush with the front in best. Mine is set back a little like some of the others, like this:

Julian is right that there are other improvements to make here, but that airdam is really well placed, and importantly, the further forward you place it, the more it will scrape ditches and bumps, the more it will beat into parking stops. Mine works great. I once diagnosed it must have broken loose and sagging by a drop in freeway MPG. I pulled over to check... and there it was... resecured it... MPG returned. For me it makes a big difference.
The aerodynamic reason you have an air dam as far forward as possible is that otherwise it helps develops lift.
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Old 05-07-2020, 06:36 PM   #14 (permalink)
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Quote:
Originally Posted by Vman455 View Post
Here are a few examples off the top of my head. Of course, the aforementioned Volt:



Also its sibling, the now-departed Malibu:



(Sorry, some of these pictures I was more interested in the wheel strakes than the air dam).

The Audi A4 uses a sectioned air dam and undertray:



So does the TT:



The Honda Clarity has this curious center air dam despite an almost completely-covered underside:



The Kia Telluride uses a full air dam, separate wheel strakes, and engine undertray:



And of course, the Mustang Ecoboost has this interesting air dam + undertray combination (this one isn't my picture):



I can't speak to why these designs are out there. Your guess is as good as mine, which is pretty worthless without any data.
Without trying to split nomenclature hairs, most of these I wouldn't call 'air dams'.

To me an 'air dam' is a device that's function is to prevent frontal airflow passing under the car. That would make the Volt and Malibu have air dams.

All the others look to me to be placed to guide or modify airflow. That's why they don't quite make sense as air dams (eg the Honda Clarity). The Kia Telluride will get flow reattachment onto the undertray behind it, for example, and so the lip might be placed to create a turbulent boundary layer that will then have better 'sticking' qualities on the rest of the underside. (That's of course just my guess.)

Thanks for the interesting pics.
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Old 05-07-2020, 07:44 PM   #15 (permalink)
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Quote:
Originally Posted by Vman455 View Post
Here are a few examples off the top of my head.
Great photos Vman. Thanks.

Quote:
Originally Posted by JulianEdgar View Post
The aerodynamic reason you have an air dam as far forward as possible is that otherwise it helps develops lift.
That might be true relative to one that is a little more forward, but I am confident that it reduces lift relative to no airdam or undertray at all.
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Old 05-07-2020, 08:00 PM   #16 (permalink)
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Quote:
Originally Posted by California98Civic View Post
That might be true relative to one that is a little more forward, but I am confident that it reduces lift relative to no airdam or undertray at all.
Do you have a photo of its placement? I have measured quite a lot of lift from an air dam placed just a bit ahead of the front axle line, with the standard flat undertray ahead of it. (Lexus LS400.)
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Old 05-07-2020, 09:49 PM   #17 (permalink)
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A quick snap I just took. The jack crushes the airdam a little and makes it look more forward and flush than it is. However, it is not as far back as I thought. Some years ago, I move it back slightly, shortened it one inch of height, and shortened the legnth side-to-side... the ends do not cover the entire face of the tire, just most of it, like some spats do.
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Old 05-07-2020, 09:52 PM   #18 (permalink)
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Quote:
Originally Posted by California98Civic View Post


A quick snap I just took. The jack crushes the airdam a little and makes it look more forward and flush than it is. However, it is not as far back as I thought. Some years ago, I move it back slightly, shortened it one inch of height, and shortened the legnth side-to-side... the ends do not cover the entire face of the tire, just most of it, like some spats do.
I'd think that would be fine for lift.
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Old 05-11-2020, 03:12 PM   #19 (permalink)
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splitter/airdam

Quote:
Originally Posted by eagle View Post
I have already installed (a relatively small) splitter in my car and am now considering the addition of an air dam



mods are made to reduce drag and not lift. but if I can lower both even better

the problem is I cant seem to get "a right answer" when I search for the air dam's possible location

a lot of racers seem to favor the "air dam above and after" the splitter meaning the splitter extends below the air dam and in front of the car



the wrc car approach is an air dam in front of the splitter



and lastly , I recently saw a bluemotion golf notorious for its "extra aero features" and it seemed to have a small air dam below and after (!) a straight area -lets call it a splitter-



I am considering the "wrc approach" to be honest but a lot of guys that run track days say that

"to get max low pressure all you need is to speed up the flow. Trying to reduce airflow at the same time will have the effect of reducing the effectiveness of a splitter. Most likely it will cause turbulence under the car and increase pressure thereby creating lift"

or

"Placing it under the splitter will have a negative effect.
Will cause the airflow under the car to become turbulent and there for slow it down and create lift.
Yes The function of a splitter is to stop air from hitting the bumper and going under the car (therefore reducing the amount of air going under and more over pushing the car down)
But it also serves the purpose of creating a a flat surface which allows air to cleanly flow underneath which speeds the airflow up reducing lift.
Having the splitter protrude down will create a lip with a low pressure zone directly behind it causing turbulence"



after the air dam I am thinking some front and rear tire spats (I have taken photos again from the bluemotion golf, rather interesting) but that is another topic

what do you guys think? sorry for the long post and many photos but I tried to include everything to be specific
What is your goal? The factory already gave you both an airdam and splitter.
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Old 05-12-2020, 06:29 PM   #20 (permalink)
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Quote:
Originally Posted by Vman455 View Post
I don't think this issue of air dams is nearly as cut and dried as a lot of people here think.

First, as Julian points out above: lots of vehicles, especially full-size trucks, have no underbody paneling and very deep air dams that extend well below the lowest-hanging components. The 2019- Ram even has an extra 2.5-inch air dam that folds down at high speeds, despite the fact that the fixed portion already extends below the lowest-hanging component under the truck:


Second, even production cars with engine undertrays, rear diffusers, and center undertrays still use air dams. I've spent years now looking under nearly every production vehicle at the Chicago Auto Show, and you all would be surprised how many cars have very smooth underbodies and an air dam, both with and without separate front wheel air dams.

Bottom line: I don't think it's prudent to rule out air dams with smooth underbodies, or to adhere to any blanket rules regarding their depth.

For reference, if the OP's car is a Fiesta--here's what the front underside looks like (on American market cars). No undertray, full-width air dam, no separate wheel strakes:
mine has a 4" air dam

the underbody is a mess btw

it looks like it has a wheel splat but it actually does not



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