Lower air dam complete!
 

What do you guys think?

http://img.photobucket.com/albums/v4...e/IMG_7945.jpg

http://img.photobucket.com/albums/v4...e/IMG_7946.jpg

Aba? :)

Not yet, but I'll get at that sometime this week. :)

Looks great!!!:thumbup:

Looks good!

Looks good! I am eager to learn results.

Sam

Congrats. And thanks for the pic. It's quite well-established on this forum that these work, so I would expect a benefit of a percent or two (nothing radical). ABA testing is a fine idea.

Any more design or build details? More pics of the process?

Looks like you might need some better support in the middle/center of the air dam. I found that my first ones folded over at speed. :(

Ok, well. This thing is too low I think. It keeps scraping on stuff. I'm going to make a new one that isn't quite as low.

I'd be happy to take more pictures. I hadn't when I was building it, but I'll do that this coming weekend when I have a little bit of time.

You might want to look into a drag actuated airdam. Someone on here has the air dam flip up out of the way at low speeds via gravity, the air flips it back down at speed.

I think the kind of testing you are doing to establish the best height is the way to go. Then a full lower pan fitted will give you the lower support you need.

Sam

It is self-adjusting! :)

X2!!! Let the ground do the work for you. That way its as low as possible for the driving that you do on a regular basis. Pair with side skirts to maximize benefits.

Can you share how its attached? Plan to make a plow for my Saturn in the future...

Going to hit search on this. What are your thoughts spaceman? Will the sides add as much as the front does? If so, I'm in. About to add front to my saturn. Did on previous CRX with the good old garden edging.

Back to OP.. I would let it scrape on those steep driveways. What can it hurt? Lower is better.

From what I have read, it kind of depends on how smooth the bottom of your car is. If it is smooth, the strategy is to get the air to flow smoothly between the wheels. If it is not smooth, then you try to get it outside the wheels and around the car. Then the challenge is getting the air to come back together smoothly with minimum drag at the back. That kind of depends on what you did at the front, and the shape of the rear. I would like to hear others' thoughts on this.

Sam

I have read repeatedly on here that only minimal improvements to aerodynamics can be achieved with the front, while the greatest difference can be had through the back. Grill blocks and air dams work. People think that nosecones will make a car more aerodynamic. They just make things worse in a cross-wind. A Kamm-back or better yet a boat-tail will allow the air to stay attached longer, leave a smaller wake, resulting in less drag.

An air dam is going to increase front area. The benefit of an air dam (from my interpretation) is to stop the air from going underneath. So if your underbody is terrible, an air dam would be good. If you are totally smooth and looking good, I would not do an air dam, as one does increase frontal area- and there is not much benefit. When I completed my final underbody (all the way back, and into the diffuser), I was done with the air dam. I'd say I removed it, but I didn't get a chance to- a giant puddle did lol.

I first suggest an air splitter, easiest to build/install, live with day to day while still helping.
Then an air dam, pretty easy to install, and only a bit difficult to live with (bumps/hills/pot holes).
Finally, a total underbody is easiest to live with, had the lowest drag w/o increasing frontal area, but is definitely the most difficult to do well.

This is all subjective to my experience, and may vary vehicle to vehicle. I am not doing a total air dam on the Insight because the underbody is so good already, and when I make it totally flat & sealed, the frontal area increase won't be worth it (in my mind).

I would note the tires are a rough spot, and including those could skew my mental calculations. It also depends what you can make work, ease/cost, and what it is worth to you. For me, Mustang vs Insight really varies the project- Insight must be dirt cheap, doesn't matter how it looks. Mustang must look decent to good, and be cost effective/worthwhile for the adventure/learning experience.

Sam Powell basically has come to the same conclusions I have from reading on this board.

Basically a full smooth belly pan is the best but takes a lot of time and material to build and I don't think its worth removing panels every time you want to jack the car up or change the oil.

Air dams aren't as good as belly pans but effectively eliminate the amount of air that can become turbulent under the car and induce drag. But just a dam on the front only blocks a certain amount of space behind it as air then enters the underside of the car behind the front wheel. Adding side skirts keeps most of the air from coming back under the car until behind the rear wheel.

Its kind of a game of numbers. Air dam scraping the ground keeps 80% of the air out that a non-dammed car would allow in and has a "shadow" of 4ft. By adding skirts you keep out another 80% (80% of the previous 80%) and increase the dam's "shadow" by the length between the tires. These numbers are for argument's sake only and have no science to support them.

So the dam does most of the work, the skirts help to maximize the effort and bring you ever so slightly closer to the benefit of a full belly pan. Dam and skirts will never be as good as a belly pan but when you weigh time, materials and maintenance hassles to the mix I think its the best compromise.

Like UltArc said though, depending on each car's underside, a dam will have varying degrees of benefits.

At least that is the way I understand it. Please speak up to tell me I am dumb when I start giving bad advice lol.

Right now my underbody is horrible. I'm doing ABA testing tomorrow on the front dam, so I'll post results on the effect it had on my car.

Ultimately, I've been cringing at the increase in frontal area and do intend on a full underbody pan when I get access to a lift. Jack stands in the driveway just won't give me the kind of clearance I need to build such a thing!

I thought the same- theres not enough space!

After I got under it and measured (lift), then got under and built one on a lift, I found that I really could do it underneath (on my ramps). As it gets colder, I will spend less time on the ground, but while it's nice out, I won't sweat as much.

And design, design, design! Mine is three pieces, rear to front. This is so there can be reasonable overlap, and the wind doesn't catch it.

At the very rear, I have the diffuser. Tucked into/out of/into/out of/into/out of/into, and attached every few feet at different points, is the rear panel. Air shouldn't be getting in my rear bumped from underneath, rather flowing along the panel. This goes from under my rear bumper to the mid of my cabin. The next piece covers that (by over 6 inches) and connects to a bar right before my front wheel wells, this is also just before I get to the engine drain plug. The final piece connects at this bar, not really overlapping but connecting to the bar so it can drop and hang from it. The beginning attaches at the very front, inside the bumper. The bumper hangs a bit lower, and I also have an air splitter helping keep the air apart (what is supposed to go underneath, and what should be pushed to the sides). The part that is attached to the bar works like a swing. So for an oil change, only the front zip ties need to be cut, the front drops down while the rear hangs up, and oil drain plug and filter have easy access.

It's been a while since my most recent build, and I don't change my own oil- but it made sense when I built it. The Ford techs have never had an issue with it, as long as they are aloud to rip out my SC&UG (EVERY F___ING TIME!!!), and remove my front seat and sit in the back (I literally fall backwards every time I get back into the car. Every time.).

It is interesting to study what newer OEM rear treatments are doing. In general I would say the Germans are taking this more seriously than the Japanese. The American designers are somewhere in between. Some designers are incorporating something like a kammback effect on the lower edge of the bumper face in an attempt to carry the bottom air past the rear flat. Others are doing just the opposite and including molded ridges that run parallel to the air flow to help it move smoothly up the back side. This would be similar to the vortex generators that are getting press these days. The kammback design is nearly universal on the upper trailing edge these days. Once you start looking at these details it gets to be sort of an obsessive habit.

Has anybody here played with the vortex generators?

Sam

I don't know anything about those.

I also don't know how much help it is to work on the underside of the rear if it isn't smooth and clean leading up to those parts.

Those are good thoughts. It would be useful to have access to testing data on how the air does flow under a car. I cannot imagine. My car has deep cross members that stick down. Does static air just hang up there or does it flow up into and out of those spaces?

There are several types of vortex generators. The most common ones are showing up just above the rear window on the roofs of most BMW sedans. I will do a search and find others and post them. Somehow or other they make the air flow more smoothly down the rear window without creating eddies and separation.

Sam

I understand them unplugging it, if they need to run diagnostics, but mechanics always remove mine, too. With the 3M tape that I use now, they would need to forcibly rip of my Ultragauge, and I am pretty sure that I would complain about that afterward, as I would need to scrape off the old tape and redo it.

It is not listed under Car MPG Efficiency Modifications Main - EcoModder or 65+ Vehicle modifications for better fuel economy - EcoModder.com. My understanding is that they actually create vortices in order to control airflow (Vortex generator - Wikipedia, the free encyclopedia seems to verify that), but they are not really DIY things, unless you have access to a wind tunnel. A Kamm-back would control airflow without creating vortices, yielding a larger difference

According to the Wikipedia page, they are actually installed on the front of a wing, not the back.

UltArc, Could you post a photo or two of your lower treatment please? I would like to see what you have done.

Sam

There is an interesting web page I will try to re-find where a guy used pieces of yarn taped to the back window to find the best placement for a vortex generator. As i understand it the goal of the kammback and vortex generator are just the opposite.

Sam

I second this.

UltArc, I would also lik to see pics of the undertray you described. :D

If you do an EM search for vortex generators, you will find multiple accounts about their inability to show any real MPG gains. Even if one does the tuft test to find the best placement, they still find them to not be useful. I don't remember where, but I saw a guy who took some CDs and bent a third on the left and right side to make his own VG, pretty cool.

Yes, if you have a kammback, the VGs are useless to you, because the kamm will allow air to stay attached for longer and force it to leave further out and down. The VGs are designed to slow down the air so that it will wrap around the back of a car easier.

*I* think that nose looks familiar...

http://ecomodder.com/forum/member-da...ivic-front.jpg

Yes, very familiar.

My air dam is shorter, far more rigid, and just as cheap. More pics in the link in my signature (as well as other stuff I did to my car). At first, mine only occasionally scraped anything, now it does more often since I lowered it a couple inches. But, it's so durable that it will take a long time to grind down and then I can get a new one for $8...

Hmmm... you've filled my mind with ideas, as I've been wanting to lower the car ANYWAY so that my wheel gaps are smaller!

RESULTS!!! ABA test today was as follows:

I used the same 4mi. course that I did for my wheel covers. 2mi up, 2mi back, then averaged. Speed was 60mph, windows up, A/C off, radio off, fan on.

(Without Air Dam)
A1: 45.10mpg
A2: 44.45mpg
A3: 44.50mpg
AVG: 44.68mpg

(WITH Air Dam)
B1: 47.80mpg
B2: 48.25mpg
B3: 48.05mpg
AVG: 48.03mpg

(Again, without)
A1: 44.75mpg
A2: 44.6mpg
A3: 44.5mpg
AVG: 44.62mpg

I took the average of the closer results: 48.03mpg is a 7.49% increase over 44.68mpg!!!

WAY better than I had anticipated. I can't wait to make an underbody tray and see what results I can get from that!
(On a side note: I was able to manage 58mpg on my way to work today... :) )