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Discussion Starter #1 (Edited)




Pictures say a lot. But step by step instructions here:
http://hikickracing.blogspot.com/2011/01/aero-mod-splitter.html

Material you need:

  • Cabinet corners x8 - $5 for pack of 20
  • Aluminum angle iron, 4 feet x1 - $8
  • Aluminum flat rod, 0.75 inches to an inch wide, 1/8th inch thick, 4 feet long x1 - $8
  • 1/16 steel cable, 4 feet x1 - $0.50
  • 2 cable crimps and 4 wire rope clips, the ones with a nut on them. - $5
  • 5mm bolts long enough to clear the splitter with washers installed, and nylock nuts, and washers x14 - $20
  • 2 bolts, out of the bolts that bolt up the factory undtray to the subframe - $1.50
  • Alumalite or Alumacorr, 62 inches by 24 inches - $100-120 for a sheet of 4x8' from a local sign store.
Total cost: 148 - 168 dollars.


Tools:

  • Jigsaw or Reciprating saw
  • Drill with 1/4 drill bit and another bit that is smaller
  • Tape measurer
  • Straight edge
  • Sharpie or other marker
Note: having just the splitter is fine for driving around, but you really should build a spoiler or get a rear wing to balance out the splitter. If you will run just a splitter, I would make it a lot smaller (4 inches perhaps) than how I have mine. Spoiler build thread here, with link to step by step in the thread
http://clubroadster.net/vb_forum/showthread.php?t=40894
 

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You need some turnbuckles on the front now to adjust the angle on that thing and keep the front stable man. IMO those cables are not a good idea and when it builds up downforce I think it will rip through those holes in the sheetmetal. They need to be anchored in something stronger like the front beam that goes from each side of the unibody frame.
 

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brontosaurus
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How sturdy is the alumalite vs 1/4" or 3/8" birch that is used fairly often? I've seen talk of the alumalite before but have no idea how rigid it is. Does it defelct at all? It has to be so much lighter than the birch.
 

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Discussion Starter #7
The cables are fine for now: the tensile strength on them is pretty incredible, as with any steel. The tabs need to be bent down, or else you'll spend a lot of time tightening the cables as you keep using it.

But yes I think you're right about the adequacy of the mounting tabs. They've held up 5-6 hours of freeway driving and a track day, but I'm going to keep checking them to see if they start to come off. The cable option gives me a lot of flexibility; I may be able to just loop it around something semi-structural. Adjustable clips can be used for when the splitter is adjusted.

Alumalite is pretty awesome. Weight to stiffness ratio is pretty good. I picked it because it would basically save me hours and hours of work laying up fiberglass. Its pretty rigid, but its definitely stronger than a piece of plywood. With wood I would laminate it on both sides; with alumalite, I feel comfortable not laminating. Its for sure stiffer than ABS plastic.

I read somewhere ABS is good for 130mph and Alumalite is good up to 160. A friend of mine tested his 6" splitter @ 160mph. Its slightly better braced than mine though.
 

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brontosaurus
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Wow I had no idea the stuff was that strong. Looks like this is the stuff use. Have you scraped it on the ground yet? I'm curious how it'll hold up to abuse.
 

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Discussion Starter #9
I'm using Alumacorr, which is supposedly less strong than Alumalite. Its slightly cheaper than Alumalite. When I got the stuff though, I immediately realized its plenty good enough. I have a sample piece of alumalite. At its small size, I couldn't tell the difference.

Alumalite is claimed 6mm, but I measure it closer to 7mm. Alumacoor is claimed 5mm, but I measured it at closer to 6mm.

I've scraped it plenty of times. Not at drastic angles, but when I misjudge dips on the road it always scrapes. Not to mention that some driveways its impossible to drive up without scraping, even at an angle.

You can edge it with aluminum edging at Lowe's like my friend did to protect it a bit more. BTW, I don't know if this is a big no-no but if you go on my blog, please do click on the ads for me :)
 

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I know you used a manometer, and found certain psi values. Any idea on total downforce? Can the manometer measure drag? No doubt this is adding downforce, but with aero, you need to be careful of what you're doing as to not add any drag.

Perhaps on your local course, you have your top speed figures, cornering speeds, and lap times all datalogged, with consistent lap times... so that you can have some proof that this stuff is working?

Sorry to be pessimistic, but from the reading I've done, as much as you can improve aero, it is even easier to mess things up. A low-powered Miata should be focused on decreasing drag and lift, resulting in ''net down-force.''

For example, I almost bought a wing for my bone-stock powered 1.6L. I came across a 3D airfoil (GTC-200) and a 2D airfoil for cheap but jumped on neither of them because while they add downforce, they add drag. Meanwhile a properly designed diffuser would reduce drag and lift, therefore increasing downforce.
 

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Discussion Starter #11
Greeentee,
your cautious attitude is well warranted. That was my main worry when building my spoiler. It might very well actually slow down my piss-weak 1.6l miata. I did cut the bumper to try and offset the drag, but in the end my vmax went up from 73.6 to 76mph. The temperatures were lower though (about 5-7 degrees), my feeling is that my vmax with the aero mods probably didn't change much. However, I'm getting on the gas a lot earlier at the sweeper leading onto the front straight of my home track. Instead of understeering off line, car tucks in nicely and responds to throttle modulation much better. Uh, I better keep handling chatter to my build thread.. anyways:

When it comes to splitters its really hard to mess things up. It'll only work to decrease drag by clearly dividing the air going up and past the car, and keeping the air going under the car a bit cleaner.

Making downforce and decreasing lift are the same thing; 10lbs of lift decreased is going to have the similar effect on grip increase as adding 10lbs of neg lift on a car that has net 0 lift at speed. I use the words negative lift and downforce but just saying lift is actually fine too, lift just means forces generated by pressure differential and can go any direction, but its less confusing that way.

I used a differential manometer and without CFD or taking many more measurements at different spots of the splitter I can't come at an accurate idea of how much lift I am making, because the air velocity increases around the side edges of the bumper and ceases to generate appreciable pressure. But the ballpark figure I have is 50-70lbs, probably more like 50lbs. Others think I'm making 100lbs. Who knows? I have nooo idea what the spoiler is generating because my second node was placed at the rooftop, where the pressure would be much lower than the pressures under the trunk area of the car. If I could convince the track officials to let me do circles around the skidpad with and without the aero mods I could probably calculate total downforce generated.

And on a side note: my spoiler (not this splitter) may not be any good at higher speed tracks. It'll take exponential amount of power to push that spoiler through higher speeds. A wing will work much better.

I personally think an airfoil at lower angle of attack is going to help more than hurt even the underpowered 1.6 miata. I'd just have to adjust front splitter so that the balance is maintained. A good way to find out is to try.. heheh.
I'm going to try to get someone to drive my current old tires (old azenis) to the track so I can do some sessions before switching over to the R1Rs I just bought. That way I'll have a whole another set of data to gauge my aero mods.
 

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Greeentee,
your cautious attitude is well warranted. That was my main worry when building my spoiler. It might very well actually slow down my piss-weak 1.6l miata. I did cut the bumper to try and offset the drag, but in the end my vmax went up from 73.6 to 76mph. The temperatures were lower though (about 5-7 degrees), my feeling is that my vmax with the aero mods probably didn't change much. However, I'm getting on the gas a lot earlier at the sweeper leading onto the front straight of my home track. Instead of understeering off line, car tucks in nicely and responds to throttle modulation much better. Uh, I better keep handling chatter to my build thread.. anyways:
This is why I mentioned "consistent driving" (lap times) as a prerequisite for any of those data points. If your driving is inconsistent, how can you point your finger to one thing or another to explain for the 73.6 to 76mph difference?

I don't think this part of the "chatter" is irrelevant if it provides feedback onto the efficiency of the splitter.

I think it is pretty easy to mess up on a splitter. Law of diminishing returns is very relevant here. An undertray, providing a flat bottom under the front increases downforce/decrease lift by the pressure differential of the air going over and under the car. Less psi underneath creates a vacuum.

+ downforce = - lift.

Now add a protrusion of 7" as in your case, and there is bound to be a GREATER psi differential, causing EVEN MORE MORE downforce, than without the protrusion. I tend to think there would be more drag with it sticking out that long.

I've read 4" as the magical number from 1) several of the fastest Miatas across the country, all are of course boosted. 2) an aero article where splitter lengths were tested on NASCARs and found that anything larger than 4" added too much drag. I'll post it if I ever find it, but on my own splitter, I did not make it protrude that far out because I do not need that much downforce. At the front of my TougeRun lip, it extends out 1.5" max and I've already noticed a lot more downforce via steering effort changes compared to before the lip and splitter. Placebo can have its effect, which is why I took the splitter off, left the TR lip on and will test the same interchange at the same 80-90 and test how the steering feels at those speeds. So far I have an idea of how it feels: 1) stock bumper vs TougeRun lip + splitter.

I am considering trimming it down as the goal is to reduce drag.

When it comes to splitters its really hard to mess things up. It'll only work to decrease drag by clearly dividing the air going up and past the car, and keeping the air going under the car a bit cleaner.

Making downforce and decreasing lift are the same thing; 10lbs of lift decreased is going to have the similar effect on grip increase as adding 10lbs of neg lift on a car that has net 0 lift at speed. I use the words negative lift and downforce but just saying lift is actually fine too, lift just means forces generated by pressure differential and can go any direction, but its less confusing that way.
Another way of looking at it that may reduce confusion…. Production cars do not produce downforce… they have drag and lift coefficients. A wing will add DRAG & reduce LIFT, which results in the term “downforce” normally attributed to wings.
I used a differential manometer and without CFD or taking many more measurements at different spots of the splitter I can't come at an accurate idea of how much lift I am making, because the air velocity increases around the side edges of the bumper and ceases to generate appreciable pressure. But the ballpark figure I have is 50-70lbs, probably more like 50lbs. Others think I'm making 100lbs. Who knows? I have nooo idea what the spoiler is generating because my second node was placed at the rooftop, where the pressure would be much lower than the pressures under the trunk area of the car. If I could convince the track officials to let me do circles around the skidpad with and without the aero mods I could probably calculate total downforce generated.

And on a side note: my spoiler (not this splitter) may not be any good at higher speed tracks. It'll take exponential amount of power to push that spoiler through higher speeds. A wing will work much better.
Spoilers are generally not as efficient as wings. Ideally, you want to decrease the wake, which is why the Autokonexion fastback is the ****.
I personally think an airfoil at lower angle of attack is going to help more than hurt even the underpowered 1.6 miata. I'd just have to adjust front splitter so that the balance is maintained. A good way to find out is to try.. heheh.
Even at 0 AOA, the APR GTC-200 still adds drag. Believe it or not, a 2D airfoil produces less drag than a 3D airfoil due to less surface area.
I'm going to try to get someone to drive my current old tires (old azenis) to the track so I can do some sessions before switching over to the R1Rs I just bought. That way I'll have a whole another set of data to gauge my aero mods.
From all the reading I've done before making an attempt at a splitter, I think what can benefit the Miata most, is reducing drag. I'd take a diffuser over a wing, and a flat underbelly. Get the air under the car to flow fast enough, and it will create a vacuum, and naturally, downforce.

Please do not take this as me trying to be argumentative, I've done a lot of reading on the topic, and you are the first who has attempted to provide any Miata-specific numerical data.
 

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looks good amigo ! very similar to my first prototype splitter. I had turnbuckles in the same rear positions you had and turnbuckles in the front too.

I think im on my 4th splitter now... the last one took a few off track adventures at laguna seca and buttonwillow before finally giving up.
 

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Discussion Starter #14
This is why I mentioned "consistent driving" (lap times) as a prerequisite for any of those data points. If your driving is inconsistent, how can you point your finger to one thing or another to explain for the 73.6 to 76mph difference?

I don't think this part of the "chatter" is irrelevant if it provides feedback onto the efficiency of the splitter.

I think it is pretty easy to mess up on a splitter. Law of diminishing returns is very relevant here. An undertray, providing a flat bottom under the front increases downforce/decrease lift by the pressure differential of the air going over and under the car. Less psi underneath creates a vacuum.

+ downforce = - lift.

Now add a protrusion of 7" as in your case, and there is bound to be a GREATER psi differential, causing EVEN MORE MORE downforce, than without the protrusion. I tend to think there would be more drag with it sticking out that long.

I've read 4" as the magical number from 1) several of the fastest Miatas across the country, all are of course boosted. 2) an aero article where splitter lengths were tested on NASCARs and found that anything larger than 4" added too much drag. I'll post it if I ever find it, but on my own splitter, I did not make it protrude that far out because I do not need that much downforce. At the front of my TougeRun lip, it extends out 1.5" max and I've already noticed a lot more downforce via steering effort changes compared to before the lip and splitter. Placebo can have its effect, which is why I took the splitter off, left the TR lip on and will test the same interchange at the same 80-90 and test how the steering feels at those speeds. So far I have an idea of how it feels: 1) stock bumper vs TougeRun lip + splitter.

I am considering trimming it down as the goal is to reduce drag.


Another way of looking at it that may reduce confusion…. Production cars do not produce downforce… they have drag and lift coefficients. A wing will add DRAG & reduce LIFT, which results in the term “downforce” normally attributed to wings.
Spoilers are generally not as efficient as wings. Ideally, you want to decrease the wake, which is why the Autokonexion fastback is the ****.
Even at 0 AOA, the APR GTC-200 still adds drag. Believe it or not, a 2D airfoil produces less drag than a 3D airfoil due to less surface area.
From all the reading I've done before making an attempt at a splitter, I think what can benefit the Miata most, is reducing drag. I'd take a diffuser over a wing, and a flat underbelly. Get the air under the car to flow fast enough, and it will create a vacuum, and naturally, downforce.

Please do not take this as me trying to be argumentative, I've done a lot of reading on the topic, and you are the first who has attempted to provide any Miata-specific numerical data.
The whole discussion on the definition of lift is moot so I won't pursue it anymore.

Whenever I use the word "downforce" I simply mean negative lift, not net negative lift or net downforce. Like 5-3 = 2, 1-2=-1. Its still decreasing by 2. I have no doubts that my car is still producing net positive (up) lift. But it doesn't matter. At a given speed 2% increase of downward force on the wheels is still 2% increase to the force of the wheels, whether its from generation of (negative) lift resulting in net negative upwards lift/downforce or it still results in net positive lift. Your goal should be always to add the most negative lift to the car (subtract lift, subtract upwards lift, whatever).

No I appreciate it. After long discussions sometimes I am proven/convinced wrong and in those situations, I wouldn't have learned otherwise without the discussion.

I don't think we're in much disagreement with anything. I did this venture to find out if it was worth it or not. My first wave of testing tells me personally that it does, at least at my home track. I'll have to do more to make sure. Yes I'm aware 2D airfoils generate less drag. I don't see why a 3D wing would generate less; the only advantage is that it probably creates more lift for applications where the airflow to the foil isn't even across the wingspan. My laptimes went from 1.02.4 to 1.02.1, once again on rapidly aging tires, slightly lower temps, rear camber knocked off from long time usage (slower), but otherwise identical. Take it for what its worth. I don't want to make conclusions until I try again at a higher temperature. I'll post up the results for sure.

As far as my vmax goes, I didn't add that into accounting for my aero effectiveness. I used sector times to judge that. Furthermore, I'm still consistent enough that my Vmax in a given session doesn't really change, and my laptimes are within several tenths of each other unless i made a noticeable mistake. Lastly, aside from the temperatures being low, I was on quickly and noticeably aging, outdated tires (I do 100+laps each track day). Aside from the slightly lower ambient air temps, I should be going slower if not for modifications added to the car.

Have you read Katz' race car aerodynamics? He teaches at my university where I did Formula SAE; he is the authority when it comes to aero. If you haven't, please send me a PM.

Anyways, in response to the points you make, summarizing
-yes I'm aware spoilers suck ballz.
-yes I'm aware 2d wings create less drag
-but I'm also aware that 3d wing's drag to lift ratio is kickass, and thats why its run (i.e. can run less AoA to generate the same amount of lift that 2D foil would make at greater angles- might not matter for lower hp cars like you said however)
-yes I'm aware an undertray and diffuser will add even more downforce. I plan to do that sometime, unless I blow away my build target times without them. I'm cheering for your build actually, if you get a manometer like the one I used please please do some testing :)
-I read some of the same articles you are talking about and from what I gather, the optimal size of a splitter depends on several things; shape of the car's nose and undertray. This confirms what some aero engineers have told me about splitter lengths. But in the simple scheme of things, in this article the splitter still increased negative lift and very little additional drag.

Things potentially limiting splitter length, aside from scraping, race regulations, material, etc.

Leverage affect:
The leverage affect is present in any aero modification. Like a see-saw, as one device adds too much downforce on one end of the car, it pushes that end down, and lifts up the other end. Apparently the end result is lower grip than what the downforce would theoretically allow. Reason 1. to optimize splitter length, especially if you don't have enough power to pull serious rear downforce or otherwise have limited rear downforce.

Drag:
Apparently what happens is that acellerated airflow starts adding drag because of underbody protrusions. The cup car's undertray isn't very smooth and has a lot of extrusions. The article also goes on to state that this effect is pretty minimal. In fact, the graph in the article doesn't show any appreciable increase in drag. I think drag is even less of a concern for the following reasons: This is for a car that has much higher velocities than a miata. Especially if you plan to have an undertray and splitter; this effect is even more negated with a smooth undertray.

Irellevant but another factor:
Because the airflow is acellerated more at the splitter, it slows down after the splitter and acts to increase pressure right behind the splitter, while the pressure under the splitter still decreases. According to the article, there is still net increased downforce. So, not a reason to keep splitters small unless our cars have really weird nose shapes like having a wing that produces upward lift right behind the diffuser or similar shape that overcomes the downforce of the splitter.

conclusion:
So what does it mean to us miata hobbyists?
I guess there definitely is a point somewhere where you can have too much splitter, even if you have matching rear downforce, but its probably really far out. Drag from splitter is not really relevant unless you have a very high horsepower car and no undertray, or some shape that counter-acts the splitter's generated downforce by adding lift right behind the splitter.

I still think 7" is fine and 4" is kind of an arbitrary number generated from the NASCAR article. Unless those guys claiming 4" (100mm) has some analysis that I haven't read, I think 4" is just an arbitrary number thrown out there. But hey, I'm just a serious enthusiast with a little bit of race car engineering experience. Professionals will know more.

All in all, especially at the lower speeds we drive at, we benefit from the front downforce. But my car may not be taking full advantage of it until I add some more rear downforce.

BTW, your post prompted me to read the article thoroughly. Thanks a bunch.
Link to article:
http://www.ricemobile.net/downloads/RCE%20-%20Articles/splitters%20diffusers%20airdams.pdf
 

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Discussion Starter #15
looks good amigo ! very similar to my first prototype splitter. I had turnbuckles in the same rear positions you had and turnbuckles in the front too.

I think im on my 4th splitter now... the last one took a few off track adventures at laguna seca and buttonwillow before finally giving up.
Thanks Slevin. I heard splitters will get destroyed pretty often :)
I know there are many people before me who've built splitters, but I just wanted to post a how-to for those who are discouraged from trying their own projects since its a pretty simple build.
 

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brontosaurus
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I've always thought the 4" length number was thrown around in miatas because or particular class rules not allowing anything larger. I do not recall which class that is though. I've never read it to be an end all number. I could be horribly wrong as I'm sure you both are tons more versed on these topics.
 

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The whole discussion on the definition of lift is moot so I won't pursue it anymore.
I think it is important for others to know the difference... so as to avoid confusion in this discussion. Not so much to correct you or anything, it seems you know a thing or two as it is. :D

No I appreciate it. After long discussions sometimes I am proven/convinced wrong and in those situations, I wouldn't have learned otherwise without the discussion.

I don't think we're in much disagreement with anything. I did this venture to find out if it was worth it or not. My first wave of testing tells me personally that it does, at least at my home track. I'll have to do more to make sure. Yes I'm aware 2D airfoils generate less drag. I don't see why a 3D wing would generate less; the only advantage is that it probably creates more lift for applications where the airflow to the foil isn't even across the wingspan. My laptimes went from 1.02.4 to 1.02.1, once again on rapidly aging tires, slightly lower temps, rear camber knocked off from long time usage (slower), but otherwise identical. Take it for what its worth. I don't want to make conclusions until I try again at a higher temperature. I'll post up the results for sure.
That's exactly why, 3D wings aren't meant to be high up in the air, the sides (since even if the middle is at 0 AOA, the sides will not be at 0, and will have extra drag) are to catch air from around the car, so 3D airfoils don't need to be so high up whereas 2D airfoils need "clean air" across the wingspan.

Anyways, in response to the points you make, summarizing
-yes I'm aware spoilers suck ballz.
-yes I'm aware 2d wings create less drag
-but I'm also aware that 3d wing's drag to lift ratio is kickass, and thats why its run (i.e. can run less AoA to generate the same amount of lift that 2D foil would make at greater angles- might not matter for lower hp cars like you said however)
3D is def more efficient as far as lift:drag, but it just goes to show you have to know what you're doing for the application. For you and I, on stock power levels, I don't think we even need to consider wings at all for the drag consequences.

-yes I'm aware an undertray and diffuser will add even more downforce. I plan to do that sometime, unless I blow away my build target times without them. I'm cheering for your build actually, if you get a manometer like the one I used please please do some testing :)
-I read some of the same articles you are talking about and from what I gather, the optimal size of a splitter depends on several things; shape of the car's nose and undertray. This confirms what some aero engineers have told me about splitter lengths. But in the simple scheme of things, in this article the splitter still increased negative lift and very little additional drag.
Again, I toss in my input for the benefit of others, if you think discussion is not meant for this thread, then we can stop that, and I can toss pictures up of my DIY splitter as well to give people an idea of more options. As of now, you can't find much on DIY splitters, and that's understandable. I found all my useful Miata-specific info from M.net and MT.net...

I was reading about the OPEL CALIBRA or something like that, which had a CdA of 0.26 (great for a street, production car). They actually raised the front of the bumper to let more air through underneath to maximize the flow...

In the case of the Calibra, the centre section of the front spoiler was lifted to allow more (yes more!) air to flow under the middle of the car, so making the total flow more parallel with the car’s long axis. This reduced the amount of air being deflected outwards by the front wheels, reducing the size of the wake and so drag.
I've always wondered why some Ferraris have an opening in the middle, seemingly to let air through underneath...now I can see why they'd do so.

Not the best example as I'm not that versed in Ferrari models:




Things potentially limiting splitter length, aside from scraping, race regulations, material, etc.

Leverage affect:
The leverage affect is present in any aero modification. Like a see-saw, as one device adds too much downforce on one end of the car, it pushes that end down, and lifts up the other end. Apparently the end result is lower grip than what the downforce would theoretically allow. Reason 1. to optimize splitter length, especially if you don't have enough power to pull serious rear downforce or otherwise have limited rear downforce.

Drag:
Apparently what happens is that acellerated airflow starts adding drag because of underbody protrusions. The cup car's undertray isn't very smooth and has a lot of extrusions. The article also goes on to state that this effect is pretty minimal. In fact, the graph in the article doesn't show any appreciable increase in drag. I think drag is even less of a concern for the following reasons: This is for a car that has much higher velocities than a miata. Especially if you plan to have an undertray and splitter; this effect is even more negated with a smooth undertray.

Irellevant but another factor:
Because the airflow is acellerated more at the splitter, it slows down after the splitter and acts to increase pressure right behind the splitter, while the pressure under the splitter still decreases. According to the article, there is still net increased downforce. So, not a reason to keep splitters small unless our cars have really weird nose shapes like having a wing that produces upward lift right behind the diffuser or similar shape that overcomes the downforce of the splitter.

conclusion:
So what does it mean to us miata hobbyists?
I guess there definitely is a point somewhere where you can have too much splitter, even if you have matching rear downforce, but its probably really far out. Drag from splitter is not really relevant unless you have a very high horsepower car and no undertray, or some shape that counter-acts the splitter's generated downforce by adding lift right behind the splitter.

I still think 7" is fine and 4" is kind of an arbitrary number generated from the NASCAR article. Unless those guys claiming 4" (100mm) has some analysis that I haven't read, I think 4" is just an arbitrary number thrown out there. But hey, I'm just a serious enthusiast with a little bit of race car engineering experience. Professionals will know more.

All in all, especially at the lower speeds we drive at, we benefit from the front downforce. But my car may not be taking full advantage of it until I add some more rear downforce.

BTW, your post prompted me to read the article thoroughly. Thanks a bunch.
Link to article:
http://www.ricemobile.net/downloads/RCE%20-%20Articles/splitters%20diffusers%20airdams.pdf
It'd also be good to be aware of splitter height. While it's good to limit air going underneath, limiting underbody airflow also causes airflow to stall at the rear, = drag. Just like you said, psi and velocity decreases after it goes under the splitter.

I've always thought the 4" length number was thrown around in miatas because or particular class rules not allowing anything larger. I do not recall which class that is though. I've never read it to be an end all number. I could be horribly wrong as I'm sure you both are tons more versed on these topics.
The Miatas I've looked at are the UNLIMITED CLASS Miatas in Miata Challenge. The 4" / 100mm figure was from a splitter article... the only one I've found that compares splitter lengths with empirical data, so I tend to rely more heavily on data when available. Of course, aero is ALWAYS application specific, so eventually there's no point of further discussion when the basics are well-understood and no further data to go off of.

FOOD FOR THOUGHT: F1 cars, as aerodynamically inclined as they seem, actually have high drag coeffiicients, and 54% of the drag is from the tires (actually most race cars have high drag from what I've read). I've read they can be around 0.74 +/-... but then again discussion of drag for those cars are irrelevant because they have the power to overcome the drag, and most of the drag is from the aero details that produce downforce... e.g. they have great lift to drag ratios.

A typical road car has 0.3-0.4 coefficient of drag, 30% of which is from the cooling system (anything that goes into the engine bay), 30% is from exterior, and the rest is from the front/rear wheels and underbelly. A properly vented hood can reduce lift just as much.

"hustler" on MT.net reported a great reduction in lift going from OEM bumper + R lip + stock hood, to a vented hood + RB bumper -- and most everyone on MT.net attributed the redux in lift more to having the vented hood instead of the RB bumper which would limit airflow underneath the car. He had no splitter on the car.
 

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Discussion Starter #19
Gotcha.
The raised undertray in the front is often for a front diffuser, or to let air into a front wing (one of those le mans type hidden ones), or to channel air into a specifically tuned section of the undertray for venturi tunnels.

I think the vented hood would definitely help reduce lift a little bit by slowing down some velocity over the hood area. It'll reduce drag by allowing some of the trapped air in the engine bay to rejoin the airflow. Sometimes though, its hard to know without testing. Its really easy to try a run and trick your body into feeling the results you were looking for. Even when it comes to testing, bias can really effect the results (and me not excluded).

I do think this discussion is appropriate. the "chatter" I was referring to was when I was talking about the handling of my car. Thanks everyone for the contributions and compliments.
 

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Discussion Starter #20
Update:
yesterday I parked into a parking stop and damaged the splitter assembly
Fortunately, the alumalite was fine, perfectly straight.. I attribute that to the fact that it can flex much before it yields. The braces all bent, but none of the hardware and cabinet corners were bent. I bent it back for now but the al. angles I used for the main braces need to be replaced.
 
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