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Aerodynamics!
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Aerodynamics!
Does anybody know where i might find aerodynamic drag figures and frontal areas for the 6872 Novas and other late 60s muscle cars? Some of the newer cars have that information in Car & Driver magazine but the old cars aerodynamic's aren't listed anywhere i've seen to date.
with a tape measure, a stop watch, and this book
http://www.amazon.com/RaceCarAerodyna ... 358&sr=81
you can do a couple of high speed runs and coast to a stop. There are formulas included that will calculate your aerodynamic drag value which is more important than cD given in magazines. You will still need a tape measure to calculate your cars total frontal squarefootage.
So it doesn't matter if you've got a cD of like .18 if you've got the frontal area of a semi. or drag number of .45 if you've got the frontal area of a prowler. cD numbers are just that. numbers.
http://www.amazon.com/RaceCarAerodyna ... 358&sr=81
you can do a couple of high speed runs and coast to a stop. There are formulas included that will calculate your aerodynamic drag value which is more important than cD given in magazines. You will still need a tape measure to calculate your cars total frontal squarefootage.
So it doesn't matter if you've got a cD of like .18 if you've got the frontal area of a semi. or drag number of .45 if you've got the frontal area of a prowler. cD numbers are just that. numbers.
Mech Engineer
north florida engine/suspension tuner
Fabrication
north florida engine/suspension tuner
Fabrication

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It might be useful to remember that any coastdown measurements will always include rolling resistance as well as aero resistance.
Aero resistance will be a function of CdA and air density.
The frontal area (A) can be measured directly.
The Coefficient of Drag (Cd) can be calculated but the rolling resistance must be removed.
The air density can be calculated from barometric pressure and temperature.
Aero resistance will be a function of CdA and air density.
The frontal area (A) can be measured directly.
The Coefficient of Drag (Cd) can be calculated but the rolling resistance must be removed.
The air density can be calculated from barometric pressure and temperature.
Thank you all for your help. I'd probably need a get out of jail free card too if i were to attempt a top speed run on any public road. Some chassis dynos, (Superflow i think), have the coast down horsepower feature from what i've read.Noob wrote:with a tape measure, a stop watch, and this book
http://www.amazon.com/RaceCarAerodyna ... 358&sr=81
you can do a couple of high speed runs and coast to a stop. There are formulas included that will calculate your aerodynamic drag value which is more important than cD given in magazines. You will still need a tape measure to calculate your cars total frontal squarefootage.
So it doesn't matter if you've got a cD of like .18 if you've got the frontal area of a semi. or drag number of .45 if you've got the frontal area of a prowler. cD numbers are just that. numbers.
 Eric David Bru
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By coincidence this is something Big Joe and others and I were just talking about in another thread about the inner fenders.
We were not actually doing any Coeffient's of drag or anything though. Just off the cuff home brew tricks.
https://www.speedtalk.com/forum/viewtopic.php?t=8430
Ed
We were not actually doing any Coeffient's of drag or anything though. Just off the cuff home brew tricks.
https://www.speedtalk.com/forum/viewtopic.php?t=8430
Ed
Thanks nosstang, that is what i was inquiring about. The Chevelle is near 25.5 frontal area with about 420 Cd and Camaro is a little slicker but has more frontal area. Thank you also "Ed". I have a magazine that has an article about Joe's "Mean Green" '70 Chevelle. It seems as though it had a tunnel ram on top of a 454468 the best i can remember. It was very fast, even now it is still impressive.

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 Location: Abbeville, LA
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i'm writting a Program that includes calculating
Drag Coefficient Cd from 2 methods=>
1Coast Down Method
2newer Method from DragStrip ET Slip
the 2nd Method is very accurate,
but only as accurate as your Inputs are
i need the following Info
1 HoodScoop Yes or No (this will later be changed to a PerCent for
greater accuracy instead of Yes/No)
2 Density Altitude in Feet at Time of Run
3 1/4 Mile ET Time
4 1/4 mile MPH speed
5 Car Weight in Lbs w/Driver included
6 Frontal Area in Sq.Feet based off of .85% PerCent of Area
example=>
Square Feet = CarWidth_inches * CarHeight_inches * .0069444 * ShapeFactor
Normal ShapeFactors: Rectangle= 1.000 Circle= .7854 Triangle= .500
Society of Automotive Engineers SAE J1263 recommends = .800 ShapeFactor
i need you to use => .850 = Baseline ShapeFactor
7 Peak Engine Dyno HP measured at 600 RPM/SEC accel Rate
Equation is deadon accurate, but only as accurate as your inputs
like if your Dyno reads the same as my Dyno and are both at
600 rpm/sec test rate
i'll run a few simulations if some of you want to compare results
Drag Coefficient Cd from 2 methods=>
1Coast Down Method
2newer Method from DragStrip ET Slip
the 2nd Method is very accurate,
but only as accurate as your Inputs are
i need the following Info
1 HoodScoop Yes or No (this will later be changed to a PerCent for
greater accuracy instead of Yes/No)
2 Density Altitude in Feet at Time of Run
3 1/4 Mile ET Time
4 1/4 mile MPH speed
5 Car Weight in Lbs w/Driver included
6 Frontal Area in Sq.Feet based off of .85% PerCent of Area
example=>
Square Feet = CarWidth_inches * CarHeight_inches * .0069444 * ShapeFactor
Normal ShapeFactors: Rectangle= 1.000 Circle= .7854 Triangle= .500
Society of Automotive Engineers SAE J1263 recommends = .800 ShapeFactor
i need you to use => .850 = Baseline ShapeFactor
7 Peak Engine Dyno HP measured at 600 RPM/SEC accel Rate
Equation is deadon accurate, but only as accurate as your inputs
like if your Dyno reads the same as my Dyno and are both at
600 rpm/sec test rate
i'll run a few simulations if some of you want to compare results
MaxRace Software
PipeMax and ET_Analyst for DragRacers
http://www.maxracesoftwares.com
PipeMax v4.70 Download Link : https://www.mediafire.com/file/viwxszuo ... 0.zip/file
PipeMax and ET_Analyst for DragRacers
http://www.maxracesoftwares.com
PipeMax v4.70 Download Link : https://www.mediafire.com/file/viwxszuo ... 0.zip/file

 Guru
 Posts: 8206
 Joined: Tue Nov 27, 2007 9:27 am
 Location: Chicago
 Contact:
Max
Having written a program to compute Cd and rolling resistance from very accurate coastdown data, I would be very interested to see how you approach the subject. I look forward to seeing your results.
I do have a few minor questions.
How does your approach compensate for changes in engine power due to changes in air density?
Do you correlate delta air density to delta power?
Do you consider the effects of air viscosity?
If acceleration and terminal velocity are critical inputs, then how do you compensate for variances in tire adhesion?
While frontal area and shape are considered inputs, what value is placed on undercar turbulence and drag?
And, the nagging problem of all simulationshow does one validate the results?
Having written a program to compute Cd and rolling resistance from very accurate coastdown data, I would be very interested to see how you approach the subject. I look forward to seeing your results.
I do have a few minor questions.
How does your approach compensate for changes in engine power due to changes in air density?
Do you correlate delta air density to delta power?
Do you consider the effects of air viscosity?
If acceleration and terminal velocity are critical inputs, then how do you compensate for variances in tire adhesion?
While frontal area and shape are considered inputs, what value is placed on undercar turbulence and drag?
And, the nagging problem of all simulationshow does one validate the results?

 Vendor
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 Joined: Sat Feb 14, 2004 4:04 pm
 Location: Abbeville, LA
 Contact:
can you email me a copy toDavid Redszus wrote:For anyone really interested in determining the Cd and rolling resistance of their car, send me an email and I'll send an excel program that will calculate Cd, rolling resistance and power required (at any speed).
maxracesoftware@yahoo.com
thanks
MaxRace Software
PipeMax and ET_Analyst for DragRacers
http://www.maxracesoftwares.com
PipeMax v4.70 Download Link : https://www.mediafire.com/file/viwxszuo ... 0.zip/file
PipeMax and ET_Analyst for DragRacers
http://www.maxracesoftwares.com
PipeMax v4.70 Download Link : https://www.mediafire.com/file/viwxszuo ... 0.zip/file