Guru_4_hire

So I have been able to find out what the coefficent of drag is. But I havent been able to find out what the frontal area is.

Does anyone know what the frontal area of a C3 specifically a 73 is?

The coefficent of drag is .40

Guru_4_hire

using the information I have about C3s and the info I can find about the ZL1. I have been able to determine that the C3 has a frontal area of around 19 sq ft.

I figured this out by using the formulas I have for power and drag stuff for finding the needed power the math looks something like this

HP = 8.702 * 10^-6 * Coefficent of drag * frontal area * mph^3

so the theoretical ZL1 is

550 = 8.702 * 10^-6 * .4 * frontal area * 205^3
550 = .000008702 * .4 * frontal area * 8615125
550 = .0000034808 * frontal area * 8615125
15809653 = frontal area * 8615125
18.3 = frontal area

That seems pretty small but since the C3 is narrow, I guess it makes sense.

Ganey

Where did you get that no.? Have only seen the cd of 68-77 once & that wasn't it. 78-79 is higher.

corvette-pilot

I have to see if I still have an old issue of Corvette Mag from a couple months back. It was the one picking the influential cars of that era. I think they picked the 78 pace car. Funny thing that sticks in my mind was they refered to it as a brick. That modern sedans are more aero. I think the article mentiond some numbers.

???

Guru_4_hire

Its a number that I have seen around a few times before.

If anybody has more accurate info I am open too it

Twin_Turbo

78 up has a higher coeff. of drag??? I thought they had a lower one with the sloped rear window. It's not only about the frontal area, rear drag is a major contributor.

Guru_4_hire

Somebody has to know about C3 aerodynamics.

Gkull? Twin Turbo? Norval? Somebody?

Twin_Turbo

All I know is that the 80-82 front is much more stable at high speeds, a lot of race cars went to that style front end or added the pace car spoiler for stability and less drag. Most of the c3 coupe race cars I've seen have converted to the bubble window and the later style bumper. The verts almost all have an open top or a hard top on them.

I just may have the data you need... I think I have a book somewhere listing the CDs for a lot of cars.

Ganey

All the nos. have been posted. The no. you are looking for 68-77 is .47 which I posted. The others 78 up are well known.

Guru_4_hire

i still would like to have an accurate number for the frontal area. I must have missed the .47 part sorry

gkull

Frontal area could be roughly figured by getting a friend to help hold a verticle board on one door side of the car at it's tallest point. Then tape measure the distance between your verticle board. Multiply width times height and it would give you a close total area.

Your wheel wells bulge will about makeup for the narrower roof compared to the rounded door bulge.

Let's just say that your car is 42 inches tall 72 inches wide = 3024 sq inches divided by 144 to get SQ feet = 21 sq feet.

Yes, modern cars are much more aerodynamic. The square (flat) rear window was a major area of drag. All a 78 or newer Vette needs is to put enough additional chin spoiler down to keep air out from under the car, use wheels that are flush and fill the wheel wells, get a rear valance air diffuser, and some kind of rear wing to balance downforce against drag and you have a 200+ mph car with 500 hp

MILO

In one of my Corvette history books, starting with 78 PAce car the addition of the front spoiler and rear spoiler help enormously with fuel economy and aerodynamics. '79's had the option for the spoilers, and '80's + had the spoiler built in. I'll try to see if any of my books state the drag coefficient with the spoilers. The spoilers were a big issue at that time.

theoUK

This is something I've been interested to find out too.
I reckon you could get a fairly good estimate of the frontal area by getting a good digital photo taken from the front. With a measurement of a particular reference point, say across the arches, you could estimate the scale of your digital photo, then split up that photo into parts and work out the area. Crude, but it would work and it'll be as accurate as the amount of "chunks" you split the picture by. I know next to nothing about photo software, but wouldn't be surprised if you could get a program that would tell you the area of a certain part of a picture.....


Don't know about the published figures, but the value of Cd depends on what you choose as the reference area - I suppose there's certain standards, but I guess the GM engineers would use the full frontal area as you'd get from the (slightly rough!) photo method above....

Then you can work out your theoretical top speed! (Which is bugger all if you have low gears like mine!)

Guru_4_hire

well by Gkull's info our 47.8" tall car that is 69" wide should have a frontal area of

22.9 sq ft.

so if the coefficent of drag is really .47 this helps out alot.

Damn that really sucks

to make a 200 mph plus 68-77 means we need to have 810 Rwhp. compared to 689 for the .4 cd comparison

This sucks.

Ganey

Frontal area is too high. I posted that too, use 19.

Guru_4_hire

cool. But I think you forgot to put the numbers in your first post. Or maybe its me.

AD2VET

I remember reading, possibly in Car & Driver, that a 78 actually had less drag going backwards.

Guru_4_hire

thats pretty funny

aharte

According Race Car Aerodynamics by Katz, a 1982 corvette has a drag coefficient of 0.36-0.38 and a frontal area of 1.8 m^2 (19 ft^2). Not bad at all.

Twin_Turbo

there ya go, lower than the others as was to be expected. Why would GM change the body work to something with a higher cd.