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Old 10-26-2009, 11:54 AM   #1
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Default Splitter question

One of the winter projects for my car is to add a splitter and canards.

I am wondering on the splitter how much difference in downforce I would get between

A) Splitter under nose with air dam below splitter
and
B) Traditional splitter as low as possible

My thoughts are that A should be more tolerant in terms of trailer loading, surface irregularities etc.

Anyone have any thoughts on what I give up with A?

I have no clue yet on what I want to do for canards. The rule says that total surface area can be no more than 172.8" square inches. Any thoughts/experience on 1 versus 2 per side? Angle of attack?
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Old 10-26-2009, 12:10 PM   #2
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B or nothing else. Its not very hard to make these quick release with 4-bolts from under the car. The lower you get it, the more it works...and they work really well when done right.
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Old 10-26-2009, 12:36 PM   #3
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Is the effect from blocking more air under the car with the lower splitter or is there some weird ground effect of a flat plane that I don't understand?

The ones that I have seen the lowest, typically have a small raised section on the center or the leading edge to let some air under, what is that for?

Does the pressure being exerted on the top of the splitter from the high pressure wave in front of the car add to the down force?
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Old 10-26-2009, 12:54 PM   #4
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I realize this is a BMW and not a miata, but the principle remains the same.
how splitters work
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Old 10-26-2009, 01:02 PM   #5
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Quote:
Originally Posted by adamhershner View Post
I realize this is a BMW and not a miata, but the principle remains the same.
how splitters work
No it doesn't...German cars are subject to different fluid dynamic properties. jk


I am about to add one below my R-pack lip. Put it as low as you dare. You are basically stacking high pressure air on top of the lip, pushing it down since (if it's low enough) the air below the lip is at a lower pressure.

Added benefit is reducing the amount of air that gets under the car, generally reducing lift. Your airdam is doing some of this already...the lip will improve it.
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Old 10-26-2009, 01:22 PM   #6
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no, it doesn't add downforce like a wing does in the rear. it makes negative lift, (less lift) which equals "net" downforce.

don't worry about the center.

when i added an air dam, only thing i noticed was my car was slower on long straights, i imagine it was due to increased drag. maybe i made it too low.

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i just run the splitter now. only reason i made the air dam was because i put qa1 springs in and didn't have the nb tophats yet. so the car was almost stock height and i was going to a big track with high speed straights. i know from spec miata's that dropping the car an inch or more (compared to stock)picks up 2-3mph on long straights.
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Old 10-26-2009, 01:28 PM   #7
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you'd get a considerable amount of more downfoce with B, and two canards of the allowed sq./in. run per side will obviously provide more downforce than just one. It will have more drag but not by much
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Old 10-26-2009, 01:30 PM   #8
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You should have noticed the car being quicker in the turns- something you're turbo can't help with. We put that ISC splitter (design is rules limited) on an ITA Miata and saw exit speeds rise nearly 5mph - from a typical 90mph exit. The straight top speed was the same- my guess due to a higher exit speed from the preceding turn.
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Old 10-26-2009, 02:00 PM   #9
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Quote:
Originally Posted by Sam Amporful View Post
you'd get a considerable amount of more downfoce with B, and two canards of the allowed sq./in. run per side will obviously provide more downforce than just one. It will have more drag but not by much
The canards are a total square inch rule,
so I can run two that 86.4" or four that are 43.2" or some combination that adds up to 172.8"

It is an autocross car, so I am not as concerned about drag as a track car.
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Old 10-26-2009, 02:07 PM   #10
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Just an uneducated (or only halfway through edumecation) guess...one large canard should be better.

You will be putting more of that surface area away from the body of the car and the slower moving boundary layer. The more surface you have outside of the boundary layer the more force they will provide.

I'm guessing they are going on the front corners...where flow is still laminar...so this is important.

It will also make adjusting angle of attack quicker and easier.
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Old 10-26-2009, 02:14 PM   #11
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all the splitter does is help isolate the volume inside the airdam, and hopefully allow some vacuum to build in there, so I dont really see why would would wnat the airdam under the splitter. I suppose it woild give you more volume to build vac in, but you would still end up wanting a splitter under that airdam too...
hmmm, double splitters
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Old 10-26-2009, 02:57 PM   #12
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One name, Bernoulli. You want stagnant (high-pressure) air above the splitter, and flowing (low-pressure) air underneath the splitter; The resulting pressure differential creates the down force.

Therefore B is the way to go. If you put the dam below the splitter a-la A, it will slow the airflow under the splitter, cause a pressure rise, and thus not work as well.
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Old 10-26-2009, 03:43 PM   #13
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Quote:
Originally Posted by Full_Tilt_Boogie View Post
...so I dont really see why would would wnat the airdam under the splitter.

cause all the vettes are doing it

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Old 10-26-2009, 03:54 PM   #14
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Quote:
Originally Posted by Braineack View Post
cause all the vettes are doing it

I'm not really sure that's what's going on in that pic LOL
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Old 10-26-2009, 04:00 PM   #15
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Yeah but the vettes do it to force air up into the heat exchangers. They are well back from the front bumper. Vettes missing that dam overheat pretty damn easy. A damn damaged dam will get damn hot too dammit.
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Old 10-26-2009, 04:16 PM   #16
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Yeah damn that Vette dam, damn it.
Cueball nailed it. On the Vette it is there for a different reason really.
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Old 10-26-2009, 04:28 PM   #17
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I know this, I was being silly.
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Old 10-26-2009, 04:38 PM   #18
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Quote:
Originally Posted by Braineack View Post
cause all the vettes are doing it

miatas have the dam there too.

also, moving the dam back near the front wheels on a street car means less scrape-age.
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Old 10-26-2009, 04:54 PM   #19
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The air dam on the c6 is different than the previous years. The reason they overheat without it is due to high pressure behind the heat exchangers created by removing this. People can't seem to grasp the concept that opening a hole for the radiator doesn't make more air go through it.
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Old 10-26-2009, 05:05 PM   #20
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Article on airdams with splitters I have had archived on my computer for quite some time. Should be a good read on the topic. Enjoy!
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File Type: pdf splitters diffusers airdams.pdf (344.3 KB, 995 views)
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