Location and height of front air dam
 

I have already installed (a relatively small) splitter in my car and am now considering the addition of an air dam

https://iili.io/JaDtwu.jpg

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

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

https://iili.io/JaDDZb.jpg

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

https://i.ibb.co/pZC6cc2/1.jpg

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-

https://i.ibb.co/GJNf9GQ/2.jpg

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

A proper full length undertray with rear diffuser will reduce drag and lift better than any combination of what you have described.

I am considering it, something like that but since the splitter is lower than the sump I am not sure how it will affect aero and cooling

baby steps, that's why I am going for an air dam first :)

also, I tried to search what material and thickness I should use
some said marine ply some said pvc , cant find a complete and documented response

So, baby steps is a fine idea. The problem with a full undertray for new people is that it is a considerably larger undertaking and there is still the matter of tuning the diffuser properly. The problem with an airdam is if it is too big, hanging down well below the lowest hanging suspension, engine, exhaust parts of the car, it will increase effective frontal area and therefore increase total drag, or CdA.

The material you use for your airdam should be hard enough to hold shape at speed and not so rigid that it will break when it scrapes something. I use a product that is intended for lawn edging and I installed it at an arc under my bumper cover that gives it support to hold shape at speed while still flexiing when it scrapes the ground in ditches and such. The material is so cheap that I was able to make several versions in succession and settle on what seemed a best design. Its length, height, arc, and placement under the bumper cover all likely affect its drag effects. We don't have wind tunnels, and our testing techniques cannot detect finer changes in drag, but my experience suggests I settled on a good shape--one I modeled on known good shapes. You can find details on my build thread and garage page (both in my sig file below).

In the end, for low drag, the undertray is better, but you can start this way. You can even just do the airdam if you don't like the hassles for working/inspecting under the car that a tray presents.

Hope that helps.

If you are interested in lowering both drag and lift, looking at what race cars do is a waste of time. Only solar race cars are interested in low drag.

There are two ways of reducing both lift and drag.

The first is to stop air getting under the car. This was widely used on old cars that had very rough undersides. A front air dam will do this (and it actually doesn't need to be sized to not increase frontal area, because Cd will usually drop at a faster rate than the frontal area increases). It should be as far forward as possible and definitely not like the pictured Golf. (That position is causing a small amount of lift).

However, basically no cars of the last decade use the 'stop air getting under' approach. Instead they use smooth floors and so gain high speed flow, that reduces pressure under the car to decrease lift. Even a front undertray alone will partly do this. (If that's your red car in the pics it almost certainly already has a front undertray.)

So if you have a car less than about 10 years old (not all cars, but most), a front air dam is subtracting from the effectiveness of what the manufacturer has already done. Improving the undertrays is, to my way of thinking, far more logical. Do you have any pics taken under the car?

(Oh yes, and I am not a fan of splitters for either reducing lift or drag.)

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:

https://ecomodder.com/forum/member-v...go-2019-03.jpg

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:

https://ecomodder.com/forum/member-v...ord-fiesta.jpg

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?

Wow, if the OP's car looks like that underneath, that's good news - so easy to improve.

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.

the fiesta posted here as a reference is a stock s or se anyway, mine is a totally different design since a custom turbo kit is retrofitted and many parts are "unique"

I will post photos of the underside/ splitter / etc a.s.a.p but I think a "undetray / tire spats" topic should be made to elaborate on the subject since I am also worried about heat retention / extraction

to continue on topic , I am thinking the same "oem look" air dam but in the front of the car ; my car on the bottom pic, see green line for air dam placement

https://iili.io/JcAfMG.jpg

Here are a few examples off the top of my head. Of course, the aforementioned Volt:

https://ecomodder.com/forum/member-v...rolet-volt.jpg

Also its sibling, the now-departed Malibu:

https://ecomodder.com/forum/member-v...let-malibu.jpg

(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:

https://ecomodder.com/forum/member-v...18-audi-a4.jpg

So does the TT:

https://ecomodder.com/forum/member-v...18-audi-tt.jpg

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

https://ecomodder.com/forum/member-v...arity-phev.jpg

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

https://ecomodder.com/forum/member-v...-telluride.jpg

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

https://ecomodder.com/forum/member-v...g-ecoboost.jpg

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.:p

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:
https://ecomodder.com/forum/member-v...ord-fiesta.jpg
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.

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.

Great photos Vman. Thanks.

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.)

https://ecomodder.com/forum/attachme...1&d=1588898724

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.

splitter/airdam
 

What is your goal? The factory already gave you both an airdam and splitter.

mine has a 4" air dam :eek:

the underbody is a mess btw

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

https://ecomodder.com/forum/attachme...1&d=1589319175
https://ecomodder.com/forum/attachme...1&d=1589318958

Well, that makes sense. They put on a huge airdam because, as you say, the underbody is such a mess.

quick fix lol

anyone still following? :(

anyway, finally managed to take pictures of the underside

looks rough and needs something, I agree

waiting for mr Edgar's book and a magnehelic gauge to arrive to take some measurements

the cover which I most certainly have to modify is this

https://i.ibb.co/ZMJQg11/image.jpg

the underside is this ; note the 1 = external wastegate pipe
2= intercooler and radiator back end

https://i.ibb.co/cX5kzGg/344.jpg

The cover looks pretty good and I'd hope the intercooler and its plumbing would fit under it. But yes, watch out for the external wastegate exhaust!

You'll be able to measure pressures easily enough in the engine bay with just the Magnehelic gauge. But you'll need to make a surface pressure measuring puck and have a reference reservoir to measure the undertray pressures - all in the book.

Yes! Still following. Looking forward to your build and your results. You purchased that underside cover? Modifying it won\'t be difficult. What material are you considering? I made mine with lawn edging like this, from Home Depot:

https://ecomodder.com/forum/attachme...1&d=1590871969

The reinforced balled end forms the bottom edge of my airdam, and with the bowed curve, attached to the bottom of the bumper cover, there is sufficient resistance to oncoming air for it to hold shape. Among its advantages, it is cheap and it flexes enough when it rubs something that it does not break, crack, or tear off the car. Very durable. Tens of thousands of miles with it now. I posted a pic earlier in this thread (the jack crushing the thing make it look further forward than it is):

https://ecomodder.com/forum/attachme...1&d=1588898724

I am waiting for the "underbody fixing/attachment kit" to arrive in order to secure it properly

next, I will fit the undertray with some tufts and will mount a go pro camera somewhere to check the flow

https://i.ibb.co/cJgXFSQ/rth.jpg

I am going to try 1) no air dam 2) "wrc style" front air dam 3) oem position air dam to see if there is any difference, along with the measurements from the magnehelic gauge I think I'll have a pretty good idea of what works and what does not :cool:

Sounds a good plan.

Interesting topic. It convinces me to look at my own car, a model similar to the Polo & Golf Bluemotion.

https://ecomodder.com/forum/attachme...1&d=1591082551

completely closed undertray

https://ecomodder.com/forum/attachme...1&d=1591082582

'airdam' is remarkably small

https://ecomodder.com/forum/attachme...1&d=1591082627

What I have never noticed are the openings towards the wheels. Purpose? Cooling?

Probably need a pic to be able to comment.

Have I done, are they not visible?

Not for me!

Strange because I see them. Have added them in the correct order as small attachments.

I can see the pics now. Openings in front of wheels are brake ducts, I would think.

Overall, looks very good.

i found some FREE ABS plastic from a car looks like it's in good shape to reuse

NOTHING beats the PRICE OF FREE

dumped on the side of the road
it's called recycling :)

if it does not work out i'll just put it in the recycling bin

looks like it came off an SUV or something the bolt holes are not damaged so it's reusable

Good to know, one more reason to close the rims.
You still see room for improvement? To me it looks like it don't need an airdam.

No it doesn’t need an airdam. I’d be looking now at the rest of the underside of the car.