Aero Questions?
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,736
Likes: 37
From: Stockton Ca
Aero Questions?
I want to use a rear spoiler on my 74 that does something useful. I'm thinking 45-60 deg. How high would it have to be to actually get into the airstream and get some downforce? The front is much easier. After I drop the ft 2" and extend ft spoiler 2", that's all I can do.
I would appreciate any info and observations, George are you out there?
Ricisan
I would appreciate any info and observations, George are you out there?
Ricisan
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Are you making your own? Are you coming over for Hot August night?
The slower the use speed the more angle required. Body rake is the #1 most important thing. Keep the nose planted and cooling works the best
Take a tip from the pro's, This is the first year of NASCAR front extended air dams and rear wings. Wings are less drag per pounds of down force
The slower the use speed the more angle required. Body rake is the #1 most important thing. Keep the nose planted and cooling works the best
Take a tip from the pro's, This is the first year of NASCAR front extended air dams and rear wings. Wings are less drag per pounds of down force
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
Take a look at the '78 Pace Car air dam and spoiler for an idea of what a fairly functional setup looks like on a C3. This package lowered the drag coef. by about 15%, and likely increased downforce by a similar number. Night and day difference in high speed handling with good aero balance. The factory did their homework on this one...
But, note that you'll need additional bracing along the center area of the dam for speeds over about 80 mph to keep the Pace Car dam from deforming significantly.
And, do both ends of the car.
But, note that you'll need additional bracing along the center area of the dam for speeds over about 80 mph to keep the Pace Car dam from deforming significantly.
And, do both ends of the car.
Drifting
Joined: Oct 2003
Posts: 1,486
Likes: 10
From: Big Pine Key FL
Are you making your own? Are you coming over for Hot August night?
The slower the use speed the more angle required. Body rake is the #1 most important thing. Keep the nose planted and cooling works the best
Take a tip from the pro's, This is the first year of NASCAR front extended air dams and rear wings. Wings are less drag per pounds of down force
The slower the use speed the more angle required. Body rake is the #1 most important thing. Keep the nose planted and cooling works the best
Take a tip from the pro's, This is the first year of NASCAR front extended air dams and rear wings. Wings are less drag per pounds of down force
Spoiler is not a Wing!!
While spoiler with have a vector pointing in the down direction from deflecting. It's primary purpose is to disrupt or spoil the airflow to prevent lift.
IMHO
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,736
Likes: 37
From: Stockton Ca
I'm on it!
George: I understand the purpose of "rake" for downforce. I plan on running 275/40/17 and 295/40/18 wheel combo along w/dropping nose
2". That should help. For a functional f spoiler I want to use rubber convayer belt for a flexiable spoiler that won't break so easy.
I can see how a wing would be better. I also know that it would need to be mounted just right to get any real help. I guess a level could be used to get the wing positioned. Any more good ideas?
I can't say about HAN, but let me get the Demon tweeked first.
Ricisan
2". That should help. For a functional f spoiler I want to use rubber convayer belt for a flexiable spoiler that won't break so easy.
I can see how a wing would be better. I also know that it would need to be mounted just right to get any real help. I guess a level could be used to get the wing positioned. Any more good ideas?
I can't say about HAN, but let me get the Demon tweeked first.
Ricisan
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
The stock Vette rear spoilers might work pretty good.
I dorked with my Demon for 4 years and I never got it 100%. Because I don't have the equipment or the ability to bench flow the metering blocks and air bleed systems.... I just bit the bullet and had this local racing carb shop fix it.
I dorked with my Demon for 4 years and I never got it 100%. Because I don't have the equipment or the ability to bench flow the metering blocks and air bleed systems.... I just bit the bullet and had this local racing carb shop fix it.
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,736
Likes: 37
From: Stockton Ca
Waiting for Exorcisim!
George: I sent mine to "The Carb Shop". It cam back w/pri float stuck causing massive overflow into venturi. $20 in 91 fuel went fast.
If I am to try a wing, it would be the last thing after the car is totally set up. If the wing isn't level, it could cause extra drag and possibly less downforce. Does that sound about right?
R
I'm on vacation, using the time to get fit and heal my numerous injuries.
Old ninjas move slow in the morning!
If I am to try a wing, it would be the last thing after the car is totally set up. If the wing isn't level, it could cause extra drag and possibly less downforce. Does that sound about right?
R
I'm on vacation, using the time to get fit and heal my numerous injuries.
Old ninjas move slow in the morning!
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
Just ot better explain this, the key to better aero / improved downforce is minimizing the air that gets under the body to reduce pressure below the car relative to that above it. The combo of a good air dam and lowering do this pretty well. The one fly in the ointment is underhood pressure, which isn't sufficiently relieved by the undersized vents behind the rear wheels on the C3. In any event, an air dam helps this situation considerably.
In concert with reducing underbody air, the addition of a functional spoiler on the rear creates both additional pressure on the top of the rear deck and a pressure drop behind the car which helps evacuate what air is under the car out the rear.
Hope that sheds a little more light on this for anyone scratching their head...
In concert with reducing underbody air, the addition of a functional spoiler on the rear creates both additional pressure on the top of the rear deck and a pressure drop behind the car which helps evacuate what air is under the car out the rear.
Hope that sheds a little more light on this for anyone scratching their head...
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Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,736
Likes: 37
From: Stockton Ca
I know it works.
Skunk Works: Any hard #s on how big and what angle to mount the spoiler? How high does it have to be to catch some air? I don't think the 4" stock spoilers actually get into the air flowing over the roofline?
I wonder if a 6" spoiler would do better?
Ricisan
I wonder if a 6" spoiler would do better?
Ricisan
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,444
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
I would find some pictures of real C-3 flat rear window race cars and see what they did. Redvetracr here on the forum might also have some good info.
I've seen a Solo II Vette with a tall Plexyglass adjustable rear spoiler. The plexyglass is so it did not impede rearview.
Kind of like the above car
I've seen a Solo II Vette with a tall Plexyglass adjustable rear spoiler. The plexyglass is so it did not impede rearview.
Kind of like the above car
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
I don't have any figures, (no wind tunnel here, yet 
) on what difference 2 more inches would make, suffice it to say you would be catching more air and thus creating more pressure ahead of a taller spoiler. What you have to watch for is diminishing returns of downforce vs. additional drag.
Pre-fastback C3's would have a bit of turbulence behind the rear window that would make them a little less efficient, so a slightly larger spoiler than the Pace Car piece may be in order, but bear in mind we're not going at speeds that completely seperate the air flow from the body here.
One thing that would make any spoiler more effective without additional height would be some fencing to trap air on the rear deck ahead of it. Some of the late C3 IMSA Vettes, such as the Greenwood Daytona, took this idea to extremes.
) on what difference 2 more inches would make, suffice it to say you would be catching more air and thus creating more pressure ahead of a taller spoiler. What you have to watch for is diminishing returns of downforce vs. additional drag. Pre-fastback C3's would have a bit of turbulence behind the rear window that would make them a little less efficient, so a slightly larger spoiler than the Pace Car piece may be in order, but bear in mind we're not going at speeds that completely seperate the air flow from the body here.
One thing that would make any spoiler more effective without additional height would be some fencing to trap air on the rear deck ahead of it. Some of the late C3 IMSA Vettes, such as the Greenwood Daytona, took this idea to extremes.
Burning Brakes
Joined: Feb 2006
Posts: 1,024
Likes: 1
From: AL
the only comment i can add is that for one of my projects in college, we took a scale model of an 84 vette and put it into the wind tunnel and got baseline readings very close to advertised. then we made multiple modifications based on theories of drag and anything we could think of to improve the baseline. we tried shaping the rear to match the boundary layer-made it worse; tried taking the wheels off and filling in the wheel wells with clay-made it worse; can't remember all the things we tried but nothing made it better. moral - much cheaper to copy other's wind tunnel or track success . . . 0.02
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,736
Likes: 37
From: Stockton Ca
Best of Both?
I'm looking for less drag and less lift. That clear spoiler will get some downforce, it will also create drag. Not racing, I'm willing to give up a little grip for a little less drag. I can always start big and trim it down a la Nascar. I'm sure someone has already done this. I hope they jump in soon.
A forum member did some experiments w/string taped to the car to see where the air flows. I hope he is reading this.
Ricisan
A forum member did some experiments w/string taped to the car to see where the air flows. I hope he is reading this.
Ricisan
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
Just thought you might be interested in this thread, if you haven't read it yet. Some very good discussion...
http://forums.corvetteforum.com/show....php?t=1419660
If you improve front downforce, you must also improve the rear, despite the drag it might cause, or your Vette could become dangerously unbalanced in high speed corners. Overall you're looking for improved handling, drag or not.
http://forums.corvetteforum.com/show....php?t=1419660
If you improve front downforce, you must also improve the rear, despite the drag it might cause, or your Vette could become dangerously unbalanced in high speed corners. Overall you're looking for improved handling, drag or not.
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,736
Likes: 37
From: Stockton Ca
Skunk Works: I like the 78 PC aeros kit, the rear is perfect. The front looks like it can be improved on by making the spoiler just a little longer/lower. A 2" extension should help the aeros and catch on parking bumpers it I'm not careful. A 15% improvement would be nice. I wonder how much better my Hwy mpg would be? Comments
Ricisan
Ricisan
Le Mans Master
Joined: Aug 2000
Posts: 6,362
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From: Brazos TX
Cruise-In IV Veteran
Cruise-In V Veteran
All things being equal (same car, same speed) a 15% reduction in drag coefficient is a 15% reduction in aero drag. Rolling resistance and drive train drag also contribute to mileage so it wouldn't directly correlate to a 15% increase in MPG. At 60 mph it maybe something like 8 to 10% but as the speed increases aero drag is a larger percentage of the drag so by 75 or 80 mph you are getting close to realizing the full benefit of than 15% reduction.
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,736
Likes: 37
From: Stockton Ca
Burners: I remember hearing that you have to double the power to get half again as much speed?
I'm thinking that a 15% reduction in cd would give a 7.5% improvement?
I know that there is a formula for this somewhere. A 5%-10% increase in mpg w/more downforce would be great. Comments
Ricisan
I'm thinking that a 15% reduction in cd would give a 7.5% improvement?
I know that there is a formula for this somewhere. A 5%-10% increase in mpg w/more downforce would be great. Comments
Ricisan
