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Suspension | Chassis | Brakes -- Sponsored by 949 Racing Relating to suspension, chassis, and brakes. Sponsored by 949 Racing.


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Old 01-26-2013, 01:22 PM   #85
EarlQHan
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Originally Posted by wbradley View Post
Creating downforce usually creates drag. How much downforce does this type of car need? Not a lot, as long as it is down force, not lift.
You can make a ton of downforce through ground effects, with little increase on drag, if any. Big wings and canards and vents and scoops may look impressive, but the biggest gains will come from ground effects. Roughly 70% of the downforce generated by modern race cars come from what's under the car, not on it.

How much downforce you want to make really depends on how fast you want to go. The % increases in downforce are directly proportional to % increases on grip. I think everyone is trying to make aerodynamics more complicated than it really is and really lose sight of what aerodynamics is for: creating a pressure differential.
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Old 01-26-2013, 01:32 PM   #86
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Originally Posted by Shankenstein View Post
Absolutely, it reduces lift! Like a golf ball, therefore woooosh! \s

The dimples will initiate a turbulent boundary layer, which will hug the diffuser further up the rear. The higher it goes, the less wake cross-section. I expect the contribution of the dimples is very low.

The main way the muffler reduces lift isby providing a smooth transition between the pumpkin and the bumper. They could have left it level, but angling it will prevent the flow from getting too caught up in the rear suspension area. I'd hope that the aftermarket exhaust kits maintain that slope, but most welders are more concerned with fitment than aero.

I completely agree with you on the muffler angle but those dimples are spot welds from the internal baffling.

There was a big to-do about the dimpled vinyl that was being sold for Motorsport use a few years ago so one of the NASCAR teams did some testing. They found the dimpled surface on a golf ball works because it a rotating body and didn't really apply or work the same on a non rotating surface.

When I'm not on my phone ill look for the article and post it up.
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Old 01-26-2013, 06:53 PM   #87
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They found the dimpled surface on a golf ball works because it a rotating body and didn't really apply or work the same on a non rotating surface.
This! I learned this in my fluid mechanic class.
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Old 01-28-2013, 10:45 PM   #88
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speaking of aerodynamics, does anyone else get this pattern on the hood when dirty?Name:  ImageUploadedByTapatalk1359427495.176420.jpg
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Old 01-28-2013, 10:58 PM   #89
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Yup!
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Old 01-28-2013, 10:59 PM   #90
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Originally Posted by dulaman View Post
speaking of aerodynamics, does anyone else get this pattern on the hood when dirty?
That picture speaks volumes.

Speaking of anyone notice.. Anyone notice how much the car really prefers clean air?

Been watching the instant MPG while approaching other vehicles on the highway. Every other vehicle I've done this with, I always noticed a slight rise in MPGs when in the turbulent draft. This car, it seems to go the other direction, and picks back up after passing the other vehicle. Granted, I haven't tried any 2" off the bumper NASCAR drafting or anything, but interesting how this car pokes its way through the atmosphere.
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Old 01-28-2013, 11:18 PM   #91
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That picture speaks volumes.

Speaking of anyone notice.. Anyone notice how much the car really prefers clean air?

Been watching the instant MPG while approaching other vehicles on the highway. Every other vehicle I've done this with, I always noticed a slight rise in MPGs when in the turbulent draft. This car, it seems to go the other direction, and picks back up after passing the other vehicle. Granted, I haven't tried any 2" off the bumper NASCAR drafting or anything, but interesting how this car pokes its way through the atmosphere.
Oh my god I've never been in a car that's been so affected by the air around it. Nasty headwind? Front end likes to wiggle around. Not even sure what passed me; not a semi truck or bus or anything, but just an SUV I think...the buffet I felt from it passing me scared the shit out me.
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Old 01-28-2013, 11:19 PM   #92
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we been sick! in the morning (after a bunch of customer work first lol!)
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Old 01-29-2013, 02:41 PM   #93
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Flat bottoms can work and work well on street cars. It just has to be engineered. It will not work well if you just slap a cover on the bottom of the car and do not change anything else. The whole cooling of the car has to be changed. Engine cooling, trans cooling, and diff cooling would all have to change. Cars are a system and need to be engineered as a system.
So what needs to change and how? I extremely interested in running something like the TRD Griffon concept both on the bottom and the rear diffuser. Gonna look weird on the street but hopefully fast on the track.
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Old 01-29-2013, 08:43 PM   #94
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So what needs to change and how? I extremely interested in running something like the TRD Griffon concept both on the bottom and the rear diffuser. Gonna look weird on the street but hopefully fast on the track.
Well it is a little more complicated than just changing something. Really thorough analysis and testing is needed. Basical engine cooling like radiators, oil coolers, and radiant heat need to be able to exit out of the top, like the hood or out the bottom. Both can be done but out the top is more common for simplicity. Transmissions and rear ends are cooled with the air under the car. If that gets covered, cooling in these areas are needed also. You could add things like NACA ducts for inlets and exit it out the bottom by creating an area with even lower pressure. Another option would be external heat exchangers to cool the oil in these areas. There are a ton of possibilities.

If you are really interested in doing this, I can give you a good direction. I would pm me though to keep the thread clean.
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Old 01-29-2013, 09:23 PM   #95
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nice to see CFD analysis guys on here, about a year ago i went through a crash course on aerodynamics and CFD, but it was with a Boeing engineer...so its a lot different to car modeling.

I really should port my 3dmax models into solidworks.
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Old 01-30-2013, 03:57 AM   #96
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How good is the stock muffler can at being a diffuser?
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Old 01-30-2013, 03:59 AM   #97
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real good my car feels looser from 5k in 4th on up in speed in all high speed corners at laguna Seca with the new exhaust. Evo X has the same design but you want to loosen them up!
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Old 01-30-2013, 12:03 PM   #98
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real good my car feels looser from 5k in 4th on up in speed in all high speed corners at laguna Seca with the new exhaust. Evo X has the same design but you want to loosen them up!

I felt this way from day 1. I went looking for a nice low profile wing that is effective and have not found it. A little thing that helped was lower the front of the car a little more than the rear. This also seems to make the front brakes bite, maybe it's just me.
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