Front air dam / valance questions

[gran racing]

How much does adding a front air dam / valance help? Especially on ITB, C and A cars, I've always viewed this as an item more for show.

Now that it is winter and I'll have some time on my hands, maybe it would be worth spending some time to add one. What cheap and fairly easy methods have you used or seen that work well. (I'm basically looking for a Home Depot solution. I do not weld nor want to pay someone to weld one up for me.) I've seen some people use the bed landscaping plastic stuff, but am not so sure about that. I'm also planning on adding brake ducts and would most likely cut holes in the air dam for this purpose.

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Dave Gran
NER ITB #13
'87 Honda Prelude si

[Greg Amy]

Funny you should ask that, Dave. I've been kinda wondering that myself before I bothered to go about fabbing one.

Most folks figure the front air dam is there to clean up the airflow, primarily underneath the car. The thought is that if you move the air aside, rather than letting it go underneath the dirty side of the car, it's less drag. Of course, parasitic drag is a direct result of frontal area, and it seems obvious that adding an air dam increases the frontal area, right?

I got to thinking about this more based on what we learned as a result of data aquisition (using an Action Digital DL-1) at the 13-hour VIR race last month. I've reviewed the data, comparing my daytime stint to my evening stint, the same car, same track, same day but with the addition of our nighttime driving lights (http://it2.evaluand.com/gti/enduro04.php). I've picked four of my fastest laps from each stint, and I found where I *really* hit the slow (2nd gear) Oak Tree perfectly and at the same exit speeds.

You know what? Those lights dropped my lap times approximately 1/2 second per lap and 3 mph top speed *just* on the back straight from Oak Tree to Roller Coaster. Not surprising, right? OK, so why is it that we expect that adding frontal area with driving lights (especially *those*) INCREASES drag, while we accept as gospel that additional frontal area from a spoiler or air dam DECREASES drag? What is it about that under-car flow that's so important?

Granted, we're talking apples to oranges with the driving lights comparison. The lights were pure drag, whereas an airdam may cause additional drag while decreasing under-chassis drag, yes? Further, that straight is a very long one and partially uphill, so it's an extreme example. However, I still think it's something to think about. I'd love to learn more about the core reasons for front spoilers and airdams, and why is it we accept the additional frontal area of them without question.

Thoughts?

Greg

[Knestis]

<hijack> Hey - I want MY data. </hijack>

The other component, at least theoretically, is increased downforce due to decreased air pressure under the car.

The concept goes that by closing off the front of the car, you create a low(er) pressure area that migrates some distance back under the car. Of course, with an IT car, the leakage is pretty massive so the effect - if there is any measurable - will be biased toward the front pretty significantly.

Low pressure under the engine compartment should have the effect of improving flow through the radiators, too.

Now, whether any of this translates into improved lap times is another question. It is pretty impressive how much decreased drag DOES improve performance.

I used to do a science demo with a simple LEGO car on an inclined plane: It starts with a finite amount of potential energy at the top, and by rearranging the same pieces (same mass, right?) so that a 3x7" plat sits at 90* to the direction of travel, I could get repeatable tests that showed 1/3 or more of the energy got used up shoving air around, compared to having the plate stuck down flat on the chassis.

The only way we'll ever really know is by testing.

Building something is going to be a pain in the butt since there are all kinds of wacky contours on the front bumper of a typical IT car now...

K

[Greg Amy]

Ah, yes, professor. But, if we *do* increase downforce, now we're increasing *induced* drag as well. And, if we increase cooling flow, we're increasing parasitic drag through there as well (the amount of cooling drag is incredible)!

I really think our low-power, relatively low-speed cars will benefit much more from decreased parasitic drag than we ever can from any negligible downforce or cooling improvements. But you're right: it's all about testing. Everything else is theory and posturing...

I think you will find that most of the airdams do very little in the way of downforce and do increase the drag on the car.
The main benefit is reducing lift on the front of the cars. If you look at a majority of the cars in IT in stock form, most will have a valence that drops from the bumper area downward at a 30 to 45 degree angle.
A good example would be a SpecRX-7 compared to an ITA first gen with a good airdam.


Another benefit would be to have a place to mount brake duct openings in the air dam in a high pressure area for better airflow to the brakes.

[Bill Miller]

Greg,

I fooled around w/ an airdam on my old AW11 MR2. Didn't have any fancy data aquisition, but did find that I lost almost 2 seconds on the long course at Watkins Glen. I didn't play around w/ multiple configurations, but couldn't really see how any design was going to get back those 2 seconds and then gain me time.

------------------
MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608

[JeffYoung]

Silly question perhaps from a non-technical person, but are we 100% sure that decreased frontal area always results in decreased drag?

In other words, is a properly shaped, but somewhat larger, frontal area that breaks and directs air in the most efficient manner better than a smaller but more blockish one?

Back when I still had some math skills and thought possibly about studying aerodynamics and aerospace engineering, I recall seeing diagrams and studies that showed a properly smoothed and contoured, but larger, frontal area resulted in a faster flow around it than a blockish one.

The blockish one created disturbances and eddies at the corners, slowing the air down at those points, causing air to pile up in front of the spoiler and result in more overall drag.

Any merit to that?

[lateapex911]

The way I see it, and air dam can never INCREASE frontal area on an IT car. The rules prevent that.

So....no drag increase can be attributed to an increase in frontal area.



------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[timrogers]

Originally posted by GregAmy:
OK, so why is it that we expect that adding frontal area with driving lights (especially *those*) INCREASES drag, while we accept as gospel that additional frontal area from a spoiler or air dam DECREASES drag? What is it about that under-car flow that's so important?

The lights were pure drag, whereas an airdam may cause additional drag while decreasing under-chassis drag, yes? I'd love to learn more about the core reasons for front spoilers and airdams, and why is it we accept the additional frontal area of them without question.


Alright Greg, lets get back to the core basics of how aerodynamic drag is calculated. Drag force = frontal area * drag coefficient. So, you need to look at your car as one complete unit or system to truely ascertain the total amount of drag that it is producing. I just went down to look at my 2 garage queen NX2Ks which have nothing but the factory air dams on them. As a WAG, I think we can put an IT legal extention on the air dam of about 2". Look at all of the junk that hangs down in that 2" zone: oil pan, suspension arms, exhaust, etc. None of that stuff is very aerodynamically "clean" and its counting as frontal area anyway, so why should we let a 120 MPH blast of air hit it? Remember also that the drag force goes up (is it logarithmicly?) You double the speed and the drag force goes up by a factor of 4 because you are not only hitting the molecules of air twice as hard, you are also hitting twice as many molecules per given unit of time.
Sure, we can't do a full underbody tray, but if we can significantly reduce the speed of the resulting airsteam that is hiting the "dirty" parts of the underbody, we end up with a net reduction in drag force. Of course at the same time we are hoping to reduce front end lift, so why not try to kill two birds with the same stone? Also, depending on the design of the airdam, (remember that with our enclosed bumpers, the airdam can start just below the nose of the car)you can try to persuade more of the air to dump to the sides or over the hood. Which way would you want the air to go? Greg, you're the pilot with data acquisition & access to pitot tubes and pressure transducers... Go to town my man! :-)

Tim

[lateapex911]

I'd like to blame the computer for this...

--------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[This message has been edited by lateapex911 (edited November 24, 2004).]

[This message has been edited by lateapex911 (edited November 24, 2004).]

[joeg]

Air Dams work on my car.

Back to back testing many many years ago on the QEW in Canada.

Dam adds at least 7 MPH to top speed. Probably a bit less dramatic on a race course because you do not have straightaways exceeding 2 miles in length.

Cheers.

[spnkzss]

GregAmy wrote :


<font face=\"Verdana, Arial\" size=\"2\">You know what? Those lights dropped my lap times approximately 1/2 second per lap and 3 mph top speed *just* on the back straight from Oak Tree to Roller Coaster. Not surprising, right? OK, so why is it that we expect that adding frontal area with driving lights (especially *those*) INCREASES drag, while we accept as gospel that additional frontal area from a spoiler or air dam DECREASES drag? What is it about that under-car flow that's so important?</font>

When we ran the 4 hour Enduro this last weekend at Summit, we got out for practice and ran some times with the lights on and lights off. The lights on laps where consitantly 2 seconds slower than the lights on times. Luckily (or unluckily in a way) it rained so we never noticed the 2 second lap drops. What we attributed the drop in time to was the draw on the alt. not drag. Obviously there is some addition to drag, but drag is not the reason you would loose .5 sec is it?

Spanky
ITC #73 '90 Honda Civic WDCR-SCCA

[Tom Blaney]

Talking from experience, I strongly believe that an airdam makes a big difference in handling especially on tracks with long sweepers (like Pocono,Summit & the Glen). Properly designed with a splitter, it improves airflow under the car, and increases front bite. I have run with and without and I always notice the difference. Plus it will give you a good place to hang the brake duct hoses that are also a good thing to have.

Considering the fact that most pro teams spend a gagillion dollars developing them (and the associated weight) they must do something.

[JohnRW]

Originally posted by joeg:

Back to back testing many many years ago on the QEW in Canada.

Probably a bit less dramatic on a race course because you do not have straightaways exceeding 2 miles in length.

Cheers.

Har. The QEW is Canada's 'Bonneville Salt Flats', although the stretch of 405 past Pierson Airport (NW of Toronto) could be a runner up - 10 lanes each way, 90+mph in the dually, pulling an enclosed 24', keeping to the far right so as not to get run over by the traffic. Man...I miss Mosport...

[JeffYoung]

Tom, thanks for the info, and a follow up question.

I am fabricating a spoiler/splitter for my car over the holidays. The spoiler is a rally spoiler developed for the car back in the late 70s (its a TR8), so I assume some develpment went into and I do admit it looks fairly "slick" rounded edges, etc.

However, it has no splitter or undertay, so I've taped on some fiber board and started laying fiberglass on top of it.

What's the best design for a splitter/undertay generally, or is it car specific? Right now, my splitter extends out about 7-8 inches on the edges of the spoiler (which is in the shape a gentle parabola), tapering to 1-2 inches in the middle where the parabola is most convex.

On the undertray side, the undertray extends and covers the entire bottom of the soiler (and therefore the car) for about 12 inches.

I could go out a lot further in the front, and a lot further in the back under the rules (my bumpers stick out a LONG ways). Is there any advantage to that?

Should I track the shape of the parabolic spoiler, or should the splitter taper as I presently have it configured?

Any advice you could give would be appreciated.

Thanks.

Jeff

[Tom Blaney]

The splitter that I use (and sell) for the CRX is made from plastic sheeting (used by the dirt trackers for fender wells) and 040 aluminum sheet. The design has changed a little from time to time to simplify mounting strength. I believe that the undertray is very important because there is a lot of turbulance caused within the engine bay so the undertray entends (within the rules) back to create a smooth area under the motor/trans area. I played with the size of the splitter and the angle and find that about 1" and level still seems to be the most effective. If you look on my site you will see the example of the unit.

To add, I did find that although my CRX is normally very neutral, when the splitter was "missing due to an off" that I developed a push on turnin that normally was never there, definatly more noticable in fast sweepers. And being the calm and collected driver that I am, I would always back out and accept my fate http://Forum.ImprovedTouring.com/it/smile.gif

www.sbmsinc.com/race_shop.html (http://www.sbmsinc.com/race_shop.html)


[This message has been edited by Tom Blaney (edited November 24, 2004).]

[evanwebb]

Hey all, I have an interesting back to back with/without air dam story. Several years ago as I was just getting into racing I took a ride with an instructor at Summit Point in his car, an early Scirocco. He was driving and things were going well on a slightly damp day until he amde a slight mistake at the exit of turn 5 and drove all four wheels off into the dirt. He corrected and came back on with no apparent problem or damage but when we came around onto the front straight again he noted that the car seemed a little slow and there was a bit more buffeting for some reason. When we got back to turn 5 we noticed his air dam laying in the dirt off to the side. So it definitely seemed to have somewhat of an effect...

[gsbaker]

I can't offer any advice based on personal experience, but it is probably safe to say that, in general, any basic dam with a splitter will help more than it will hurt.

It's too bad there aren't more rules of thumb racers can use. A good friend is a consulting mechanical engineer who does a lot of computational fluid dynamics (CFD/computer simulations of gas flow). Unfortunately, that stuff gets very complicated.

Gregg

[Greg Amy]

Good info, all. Don't know if you've noticed it over the years, but I'm not one to accept "common knowledge" as The One Truth (no duh, they say.)

Bill, I don't quite understand if you lost that 2 seconds WITH or WITHOUT an airdam on your MR-2? (Man, what I wouldn't give to drive a second-gen MR-2 in ITA. I've always been a big fan of that car...)

JeffY, parasitic drag is definitely a function of frontal area, so decreased frontal area will result in less drag, all other things being equal.

Jake, you most certainly CAN increase frontal area with an air dam; the rules allow it to go as low as the bottom of the wheel, and that is most definitely lower than any production car part. Imagine going over a speed bump if your undercarriage was only 4 inches off the ground (225mm times .45)!! It can even go down another 1/2 inch or more, given we can all run 15" wheels.

Tim, good points on all that nasty stuff hanging down. I'm confident that an airdam cleans that up. What I'm really curious about, though, is how much drag is that versus the additional frontal area of an airdam? If you look at the dam I fabricated last year (http://www.gatm.com/cars/nx2000/spoiler.html) you'll see that I added at least 4 inches to the front of the car (it's the amount of the pink part which sticks down from the factory spoiler). That didn't even maximize the rules; I think I could have gone another inch.

Tom and Evan, your experience is very valuable. Thanks. Tom, where's your web site? I'd like to see some photos.

(On a side note, I remember the first time I saw Tom's spoiler/undertray. It was at the 2002 OMP Challenge, I think, and the assembly was in the cabin of the car while it was on the trailer in the infield. I saw the undertray part and thought, "that CHEATIN' b*****d." Then I re-read the rules and thought to myself, "that CLEVER b******d.")

I am confident that a front spoiler, especially when coupled to a partial undertray, is likely an advantage. I'm just not accepting that as gospel; I really want some proof...

GregA

[gran racing]

I too am one of those who question things. What I was thinking about tonight is if there is a point (car & speed) when the front air dam has a negative effect. Someone mentioned that fact that pros do it and spend tons of money developing it. I agree that based on this it seems like it would make sense for us too. BUT there has to be a point where the added weight to the front, drag, ect. out weight the benefit gained. I guess that's why I specified A, B & C cars. I know the line isn't so clear.

What is kinda funny (or maybe not) is that right next to my computer I have the 2003 GCR. On the back cover, they have pics of cars. It is interesting to see the AS not have an air dam. I know, that means nothing...

Tom - thanks for sharing the information. I went to your site but only found your professional info. not race info.

The undertray is interesting. A while back when I was first starting to build my car, it came with an undertray. I didn't give it much thought and yanked it out. Besides, it made working on the car a pain in the arse. But maybe it wasn't such a silly thing. Hmmm.

(I really need to stop thinking about racing so much. And my wife thinks I'm obsessed?)

------------------
Dave Gran
NER ITB #13
'87 Honda Prelude si

[Geo]

Dave, that under tray is critical for cooling. It increases the pressure differential between the front and back of the radiator increasing flow through the radiator. Without it, air moves from under the car up behind it decreasing the pressure differential.


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George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com

[lateapex911]

Yes, mine was mangled, and it didn't make it back on the car one time. I was reminded that it is needed to be legal. Ooopps. What a pain it was finding another one, and IT is a piece o crap!

Your wife is cool, watch the obsession!

------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[timrogers]

Originally posted by GregAmy:
Tim, good points on all that nasty stuff hanging down. I'm confident that an airdam cleans that up. What I'm really curious about, though, is how much drag is that versus the additional frontal area of an airdam? If you look at the dam I fabricated last year (http://www.gatm.com/cars/nx2000/spoiler.html) you'll see that I added at least 4 inches to the front of the car (it's the amount of the pink part which sticks down from the factory spoiler). That didn't even maximize the rules; I think I could have gone another inch.
GregA[/B]
Greg, the only real way to find out how much air dam is too much is through testing with an adjustable air dam and splitter combination. If you were to put vertical slots in your current air dam on which you could have the fasteners of a lower piece of the same shape slide up and down on,(with an adjustable splitter attached to the bottom, of course) you would have a great testable contraption.
Now, here is where the fun begins. I guess you could test for top speed first while taking it easy through the corners, to get a handle on your overall drag. The reason for this is that with a splitter, you can really start to make some significant downforce on the front of the car and make it want to swap ends in high speed turns. This has been a proven fact with the SE-R Cup guys out in CA.
Once you have a baseline for which airdam depths and splitter settings have a given relationship with top speed, then start tuning the airdam in concert with suspension settings to avoid getting a panoramic view of the high speed turns at your testing track while searching for faster lap times.
The problem with this method is that you need a track with a pretty long straight so that your corner exit speed does not affect your speed at the end of the straight.
For giggles, you can go to http://www.getfaster.com/
and click on "Road Racing" then "Tech Tips" then "Physics of Racing Series" to get to the "Speed and Horsepower" section. It shows some good calculations and knowing that the NX2000 has a factory quoted Cd of .32 and I estimate the frontal area at about 20 square feet, you can do the calculations and then wad them up and throw them in the trash as they do not take into account that we race with the windows down.
http://Forum.ImprovedTouring.com/it/smile.gif
Actually, once you find out your top speed, you can look at your dyno chart and compute what your racing Cd is. http://Forum.ImprovedTouring.com/it/biggrin.gif

[Tom Blaney]

Being that I make the spoilers, and I have a pretty reliable and consistant car/driver package (except for the occasional drama queen episodes) I have modified the size of the splitter lip to see what the effect is (also that's why one or two of them were left on the track or dragging under the car while the race progressed http://Forum.ImprovedTouring.com/it/frown.gif) And as noted I am a fan of rules compliance, the splitter lip can't protrude past the front bumper I found that a consistant 1" lip all the way around seems to work the best. I did try a 3" lip once and it got pulled off of the car within a few laps indicating that there was a lot more downforce being generated and perhaps too much since all it will do is create drag. Keep in mind that the splitter is doing double duty (not including grass trimming) it is reducing frontal drag and increasing downforce on the front end, too much downforce may seem good for a F1 car but were talking about < 150hp in our cars. Bigger is not always better ..

This is a photo of the airdam
http://www.sbmsinc.com/photos/airdam_0.JPG

This should take you to my site
http://www.sbmsinc.com/race_shop.html

[This message has been edited by Tom Blaney (edited November 25, 2004).]

[This message has been edited by Tom Blaney (edited November 25, 2004).]

[jlucas]

Originally posted by timrogers:
[quote]knowing that the NX2000 has a factory quoted Cd of .32

"Factory" posted Cd number are... shall we say... optimistic.



------------------
Jeremy Lucas
Team Honda Research
Kumho - Cobalt - Comptech

[Bill Miller]

Greg,

I lost the time w/ the airdam. And it was a 1st gen. (AW11) MR2. Be a great ITB car. All four corners are totally adjustable for camber/caster/toe, not to mention that everything mounts on subframes. I used to have a full set of corners that I'd take to the track. I missed out on the last race at Bridgehampton because I broke an inner tie rod, and couldn't get a replacement. After that, my moto was, if I had it, I brought it!

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MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608

[Knestis]

A coast-down test is a great, repeatable way to determine the drag hp of an entire car's package. {It's a negative number, in vehicle dynamics terms.)

It doesn't require the kind of space that a top-speed test does and can even be done on public roads: Another argument for street-legal IT cars. http://Forum.ImprovedTouring.com/it/smile.gif

K

[gran racing]

That's interesting Bill. MR2 Jake recently put an air dam on the car and got his best time at Lime Rock. There are a lot of factors that were not taken into consideration and the air dam may not have contributed to this. (Other factors like me being in front of him and he just can't have that.)

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Dave Gran
NER ITB #13
'87 Honda Prelude si

[Bill Miller]

Dave,

I don't think you're getting to the same terminal velocity at LRP as on the long course at the Glen. I really seemed to notice it at the end of the back stretch, going into the bus stop. Not to mention that lap times at the Glen are ~2.5 times what they are at LRP. With the longer distance, even small reductions in velocity will have a big impact on lap times.

But again, the air dam design certainly wasn't optimized, or even modeled.

------------------
MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608

[ITANorm]

Originally posted by Bill Miller:
Greg,

I fooled around w/ an airdam on my old AW11 MR2. Didn't have any fancy data aquisition, but did find that I lost almost 2 seconds on the long course at Watkins Glen. I didn't play around w/ multiple configurations, but couldn't really see how any design was going to get back those 2 seconds and then gain me time.



Bill,

Not to mention that if you start monkeying about with the airflow under an AW11 (at least in IT-legal configurations), you will start having issues with engine bay temps. (Which will lead to clutch hydraulic vapor-lock, etc.)

[dyoungre]

Just a few 'theoritical' points:

Frontal Area: take a picture of the car directly from the front - it is the 2 dimensional projection that you see. Going lower witht the airdam may increase the literal area, however:

Airflow over versus under the car: Think of what the big deal in F1 wind tunnels is with the 'moving ground plane'. As an analogy, think of a main bearing - with the crankshaft surface doing 70 mph. The oil right at the crank surface is doing 70 mph, and the oil at the block is doing 0 mph. In between, the oil is shearing, which is drag. Same hold true for the air under the car - the air trapped in the exhaust tunnel, around the gas tank, anywhere on the underside surface is going 70 mph, while the air at the ground is going 0 mph. That difference in speed occurs in a much shorter distance than if the ground weren't there (or if it were moving at the same speed as the car, like in a wind tunnel without a moving ground plane), and so the shear effect, or drag, is much greater.
As someone said before, it the pressure (or looked at another way, the density) of the air under the car that can be reduced by an air dam by getting the air to flow over (creating downforce, or eliminating lift) or around your car.

On the 79-80 RX7, there is a lot of lift, even at 70 mph, because a lot of air is forced UNDER the bumper instead of over it; Mazda reshaped it for '81. My airdam changes the high speed handling enough to cause me to adjust my sway bar setting - equal to removing the stock rear sway bar. My experience agrees with what others stated - the biggest difference I saw with/without the airdam (after I lost it in turn 11 at NHIS) was about 60 deg F in radiator cooling. For your Honda, that could mean the difference between your fan being on or not (alternator current draw), or you could potentially reduce the size of the opening, which should reduce drag. The devil may be in the detail, but I think that it is worth trying, even without an F1 wind tunnel.

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Dave Youngren
NER ITA RX7 #61

[Nigel Stu]

There are some interesting articles in the last 2 issues of "RACECAR ENGINEERING" (at least that's what I think its called... someone please correct me if I'm wrong) that talks about airdams and splitters. Good reading if you can find it in your area (UK print, I have been able to find this mag at B&N and Borders in the Detroit area)

[Racerlinn]

Back to Dave's original question.
I have had good luck working with vinyl house soffet. Has a good smooth surface and is easy to work with, both cutting and with a heat gun to make bends. Just don't over-use the heat gun, the vinyl will shrink and yellow. Practice makes perfect. Plus it's cheap, less than $10 for a 12 foor piece. But it does not take paint well, so you better like the color white... (see below)

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Steve
'92 ITA Sentra SE-R
www.indyscca.org
http://img.photobucket.com/albums/v366/Racerlinn/ITA6b.jpg

[gran racing]

Easy to work with and cheap work for me!

Where could I find this? Would a home depot or Lowes carry this stuff?

I can't tell from the picture - do you have a splitter as well?

Thanks.

------------------
Dave Gran
NER ITB #13
'87 Honda Prelude si

[Racerlinn]

I've not been bold enough to try a splitter yet, I have enough on my plate right now making sure the car will be ready for spring. Here's a good sample of a low budget one (that I hope to someday boldly copy on my own): http://www.nissport.com/spoiler/default.asp
Thanks Geo and Grover!

As far as soffet (or soffett?) you will find it at most home improvement "speed shops". I use my unofficial "sponsor" Lowes. It's back with the flashing and gutters. Generally it has some ribs similar to vinyl siding, but the flat sections are about 4" wide. I use the heat gun to bend a nice 90 degree flange to use to bolt it up to the bottom of them bumper cover. I put a small, tight 180 degree curve on the bottom edge for rigidity. The hardest part is to conform to the curves at the side of the bumper, wrapping around to the fenders. You have to notch out the top flange in multiple places to get the vinyl to properly curve. Again, practice makes perfect.

My unsubstantiated, underengineered, set of the pants opinion: I think the front of car feels better at highway speeds. More drag? Maybe. But I agree with others like Tim that I would rather have the clean front edge rather than the air hitting the bottom of the tranny, motor, etc.
------------------
Steve
'92 ITA Sentra SE-R
www.indyscca.org (http://www.indyscca.org)
http://img.photobucket.com/albums/v366/Racerlinn/ITA6b.jpg

[This message has been edited by Racerlinn (edited November 30, 2004).]

[bill f]

Boy, I hate to admit to an advanced age, especially one that would allow me to remember this!

In 1975, during the infamous "gas Crisis", Car and Driver did some early testing of wind cheating devices to see what would enhance gas mileage. Their base test sled was a '75 Pinto 2300cc engine, with automatic transmission (more were sold than 5 speeds at the time, I believe). It was done on an instrumented car, at 75MPH, as I recall, on one of the southern Super Speedways...Talledega, perhaps?

Besides using headlight covers, blocking off the grill, then varying detrees of open, using an add-on rear spoiler, they also fabricated an air dam with wrap around edges, which extended down from the already vertical bumper.

Relative to the front air dam, the conclusions ran along these lines:
The LOWEST, deepest dam was the most effective. They began with a dam which was almost touching the pavement, and had to eventually trim the dam to allow for driveway clearance, only. Trimming was proved to diminish the effectiveness of the dam. I repeat: Lowest was the best.

Their explaination (theory, at the time?) was that the air drag from the additional frontal area was still less than the under-chassis drag from the "dirty" underside of the car. Cleaning up the underside (blocking off the air source) reduced the drag beyond the addition of drag from the increased frontal area.

Incidentally, the combination of devices they worked with (basic materials, with hand tools) gave and additional 25% boost in gas mileage.

I kept a copy of that article for years, as I was building a B Sedan Pinto, and copied their work. They then went on to evaluate various devices on a few other cars...I remember the Datsun Z car with commercial air dams used.

Not promoting any position here, only reporting what I remember of the article.

Good racing.

Bill

[Knestis]

I'm reviving my old rallying tradition of celebratory motorsports limmericks, for your listening pleasure...

A budget-wise racer named Moffet,
built airdam and splitter from soffit.
Took weeks, the poor dope,
so he'd better hope
that he don't hit a curb hard and off it.

K

[lateapex911]

touche'

------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[Racerlinn]

Originally posted by Knestis:

A budget-wise racer named Moffet,
built airdam and splitter from soffit.
Took weeks, the poor dope,
so he'd better hope
that he don't hit a curb hard and off it.
K


Yep, that's me!! I've already gone thru two version in the last few years wacking cones. But I can make one in a couple hours now.


------------------
Steve
'92 ITA Sentra SE-R
www.indyscca.org
http://img.photobucket.com/albums/v366/Racerlinn/ITA6b.jpg

[Geo]

Originally posted by Racerlinn:
I've not been bold enough to try a splitter yet, I have enough on my plate right now making sure the car will be ready for spring. Here's a good sample of a low budget one (that I hope to someday boldly copy on my own): http://www.nissport.com/spoiler/default.asp
Thanks Geo and Grover!

This one is actually quite strong.


------------------
George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com

[gran racing]

Well it is good thing I never go off being too aggressive. http://Forum.ImprovedTouring.com/it/rolleyes.gif

I also need to figure out how much lower I could go with my "trailer" and not destroy it then. I can just picture spending hours on the thing then taking it right off as I load the car for the first time.

------------------
Dave Gran
NER ITB #13
'87 Honda Prelude si

[67ITB]

Dave,
You can make it easily detachable and you don’t have to worry about trailer clearance.
As long as you have room in the tow vehicle? Or if it can some how fit in the car itself?

And that is you can make it “detach easily”, NOT you can “easily make it detach”
As that part of the design took a little more thought process than I realized going into it, but we were still able to get it done

Matt

[Diane]

Dave,

Mine is detachable. Let me know when you are in this area and I can show you. Or I'll drive it to work some day and you can get some new bike gear for next MTB season. http://Forum.ImprovedTouring.com/it/smile.gif

Diane

[gran racing]

Detachable? That means I'd have to attach it too. So I'm a bit lazy. I'll have to check out what you did with your car.

Mt biking...just picture 4 racers getting together for a "leisurely" ride. I'm so glad none of us are at all competitive.

------------------
Dave Gran
NER ITB #13
'87 Honda Prelude si

[Greg Amy]

This is great information, but it pisses me off; now you've taken away my excuses for lack of motivation of building one...

Dave et al: detachable is easy. Six to ten quarter-turn "Dzus" fasteners in key locations ought to do it...

[Diane]

Originally posted by gran racing:
Detachable? That means I'd have to attach it too. So I'm a bit lazy. I'll have to check out what you did with your car.

Mt biking...just picture 4 racers getting together for a "leisurely" ride. I'm so glad none of us are at all competitive.




Yes, it does mean you have to attach and detach. http://Forum.ImprovedTouring.com/it/tongue.gif I could however go over speed bumps with it *slowly* but rarely used it on the street. Never in the winter of course, but I'd install it to show you (even though I know it won't clear the driveway to the shop http://Forum.ImprovedTouring.com/it/wink.gif ). I want to say it's maybe 10 fasteners? It's flexible enough to stow in the car for the trip to the track.

As for non-competitive mountain biking, what's that? My bruises say otherwise. http://Forum.ImprovedTouring.com/it/biggrin.gif You forget to mention 4 *IT* racers.

[slackerjay]

here are a few great ideas from another site on making a splitter.

happy holidays

http://honda-tech.com/zerothread?id=930543

~jay

[Boswoj]

Couple of things to throw on the pile:

When Mario won his World Championship it was at least in part due to the radical approach to "ground effect" aeodynamics. He was at the forefront of a spectacular wave of development intended to increase grip through aerodynamic downforce, without the huge penalties in drag imposed by wings. I was reading an engineering brief comparing current F1 cars to their counterparts of the late 70's and early 80's and I was shocked. If you think that todays F1 cars are the absolute pinnacle of technology, you would be wrong when it comes to aerodynamics. If you look at the downforce/drag ratio of current wings it's about 1.2 to 1.4, meaning for every pound of drag you get something like 1,4 pounds of downforce. With a smooth, clean, well designed underside with tunnels and diffuser like in 1978, you get SEVEN POUNDS FOR EACH POUND OF DRAG! Experts postulate that a modern F1 car with full ground effects would be in excess of seven seconds faster a lap with the addition of this "old school" technology. Even on a low HP car, you are pushing a "whoopie cushion" of turbulent high pressure air through the convoluted and aerodynamically "dirty" undercarriage of your car creating drag and causing lift. Does anyone remember Smokey Yunick putting 600 pounds of bondo on the underside of one of his his famous Nascar "rule-stretchers" to clean up the airflow and gain advantage on his less inventive competitors?

Happy Holidays - Boswoj

PS - As a sidenote, that same Smokey is the reason NASCAR has templates today. He showed up to race with a hand-made 7/8ths size replica of a production stock car because it saved him 12.5 percent of the frontal area of a real car! Took a while before someone noticed - but there wa a lot of hollering afterward!

[This message has been edited by Boswoj (edited December 24, 2004).]

[Knestis]

I've been playing with the analysis software that came with my DL1 and it has a clever utility that uses two sets of coast-down data (high- and low-speed, easy to collect, now!) and vehicle mass to compute the sum of aero and rolling resistance drag - in negative horsepower.

This just get cooler by the minute...

Then, once those figures have been established, the system can do the math the other way to determine positive (engine) power, based on on-track performance - even correcting for ambient temperature, pressure, and relative humidity.

K

[Racerlinn]

OK, get ready, here it comes.......
I got a wild hair (plus it was a balmy 40 degrees here over the weekend - perfect time to work on the car) so I took a stroll thru my favorite speed shop (aka Lowes Home Improvement). In the HVAC aisle, the always-a-fan-favorite 3" flexible aluminum ducting was procured. After a wander thru the hardware, paint, and flower arranging sections, I made my way down to Siding and Guttering. A pair of plastic 3"x2" gutter spouts later, I was in the checkout line spending the balance of my X-Mas gift card - about $12.00.
Here's the results of $12 and an hour and half of free time in the garage.
Ducting the drivers side was pretty darn easy. Lot's of room next to the tranny, lot's of clearance from the wheel, and the wheel well splash shield makes a nice mounting "bracket" for many zip ties. The passenger side is a different story. Just like traveling the the roads in Pennsylvania, you just "can't get there from here". I finally decided that a decent trim of the splash shield would allow as high of routing of the duct as possible along the edge of the oil pan. The duct on this side is now the lowest hanging part of the car and is sure to take a beating. Plus, when at full left-hand steering lock, it made the nice 3" diameter tube into a 2"x4" rectangle. Hopefully the differential of air flow from the added restriction does not cause to much of a balance issue for the brakes (hmm, will Steve by consistently locking the drivers side wheel this year?) But, for $12, what the heck. The results:
Air dam (installed in my vinyl siding air dam):
http://img.photobucket.com/albums/v366/Racerlinn/6dd2dc9e.jpg
Drivers side duct:
http://img.photobucket.com/albums/v366/Racerlinn/16da20a7.jpg
Passenger side duct:
http://img.photobucket.com/albums/v366/Racerlinn/fbdde1cb.jpg
Let the pointing and smirking begin!

------------------
Steve Linn
'92 ITA Sentra SE-R
www.indyscca.org (http://www.indyscca.org)
http://img.photobucket.com/albums/v366/Racerlinn/SideSER2.jpg

[This message has been edited by Racerlinn (edited January 31, 2005).]