big red aero?

[RobM]

Now I’ve always been told that first gen camaros need a ton of aero work to even go 150 mph in a stable manor…but after reading about big red and seeing some good pictures it doesn’t seem like that car has too much work done to help it cut through the air other then a very large amount of power…I may be wrong here so correct me if I’m wrong. Does any one have any opinions on this? From the looks of things it looks like the body is pretty stock and this thing has been hurled to 220 mph.

[MrQuick]

Hi Rob,
you can actually defeat air resistance by either having an insane amout of horsepower or a big pair of brass ones...in which case Big red(Clifford) has both.

[Payton King]

I spoke with Stielow a few years back and he had seen the car. What he told me that what was lost in photos was how low the car is. He also stated that they had dropped the nose in the front and "pie cut" the back of the fenders to get it to work.

[Steve1968LS2]

didn't they tape up the front before the really high speed runs? I thought I saw a picture..

Remember.. air pressure doubles every 15mph.. that is why it's pretty easy to go 150 and really hard to go 200mph..

BR is one bad ass ride..

[BuddyP]

yup, air resistance increases times 4 everytime you double your speed.

[Steve1968LS2]

yup, air resistance increases times 4 everytime you double your speed.

Funny.. I remember it as doubling every 15 mph..

Either way.. that's a LOT of air to push through at 200mph..

If 15 mph = 10

then 150 mph = 5120

and 210 mph = 81920

Just to give you an idea of the difference just a tiny bit of speed makes once you get going fast

[alcino]

funny, fuelie beat me to the math.

[Fuelie Fan]

F_drag = ½ * Cd * rho * A * V^2

Cd = drag coefficient
Rho = air density (4.67E-5 lb/in^3)
A = frontal area
V = speed

For a stock 69, Cd and A are 0.4 and 25.1, respectively

Doing unit conversions

F_drag (lb_f) = ½ * Cd * (4.67E-5 lb/in^3) * A(ft^2) * V(mph)^2 * 115.44

For a camaro F_drag works out to 0.027 * V(mph) ^2

Road power to overcome drag P = F*V

Again with units…

P(hp) = F(lb_f) * V(mph)/375

So:

Speed Drag Force Drag Power
50 mph 67.5 lbs 9 hp
100 mph 270 lbs 72hp
150 mph 607.5 lbs 243hp
200 mph 1080 lbs 576hp

Note that the power actually goes up with velocity CUBED. Also note that numbers above are for aerodynamic drag ONLY, other factors will raise the hp require, such as tire losses and increasing drivetrain losses with speed. Also, that is not a crank power number, it's a rear wheel power.

[Steve1968LS2]

Isn't that what I said.. only in english ;)

[shmoov69]

What the!??!?!
Sorry, I slept thru that class, or year for that matter!
So, in my 69, before the turbo's, on a chassis dyno the wheelspeed was 170mph at 6100rpm. I have had the car on the road (LIKE AN IDIOT!!) at 6200rpm. What kind of speed is that after the drag?
I am by no means smart enough to figure that out by your greek above!

[alcino]

shmoov69- for what you want to know you don't need to know anything about drag.

new speed = old speed / old rpm * new rpm

~173mph

alcino

[Zefhix]

I also recently asked about this formula because I wanted to know based on my combo what actual MPH my car would resonably achieve based on HP, Wheel diameter, ratio of OD and drag coefficient. I know that the coefficient of drag on my 70 Chevelle is .47 based on a lot of looking. My tire diameter is 28.78, Trans OD ratio is .70:1, rear ratio is 3.42:1 and Hp is 650 at the fly. the only figure I don't know is front area..any of you want to take a stab? I'm curious to know where the car will be at (MPH wise)in 4th at 5500 and 6000 Rpms realistically. Thanks-

[Marcus SC&C]

Numerically it comes out to 197mph at 5500rpm and 215mph at 6000rpm. I`ll leave the aero calculations to the pocket protector types but my S.W.A.G. would be an aero limited 180mph. With some aero mods maybe 190mph? Marcus

[zbugger]

I also recently asked about this formula because I wanted to know based on my combo what actual MPH my car would resonably achieve based on HP, Wheel diameter, ratio of OD and drag coefficient. I know that the coefficient of drag on my 70 Chevelle is .47 based on a lot of looking. My tire diameter is 28.78, Trans OD ratio is .70:1, rear ratio is 3.42:1 and Hp is 650 at the fly. the only figure I don't know is front area..any of you want to take a stab? I'm curious to know where the car will be at (MPH wise)in 4th at 5500 and 6000 Rpms realistically. Thanks-

Only as fast as the driver's balls are big....

[shmoov69]

shmoov69- for what you want to know you don't need to know anything about drag.

new speed = old speed / old rpm * new rpm

~173mph

alcino

No, what I was asking was the actual speed on the road at that RPM? After the drag and such.

[Fuelie Fan]

Assuming Cd = 0.47, frontal area = 25.5 (from smokemup.com), drivetrain losses at 25%, and the power curve we came up with on desktop dyno:

You can make 150 in 3rd at 6000 with power to spare. When you hit OD, your rpms will drop into the 4's, and you won't pull past 160. If you had a rear end ratio of roughly 4.3, I think you'd hit 174 at 6100.

If you drop your Cd to 0.42 (which is what smokemup shows) and go to 4.11's, then you should be knocking at the door of 180 at 6000.

All of this is of course sensitive to your final Cd and frontal area, but it seems like your gearing is your limit to speed

[Zefhix]

Wow, I love math...it always proves itself!! It funny that my lack of steeper gears is limiting my top speed because you'd think exactly the opposite!! 160 should be fine besides, I got some kick ass guy building me a special FI system to feed my car and another kick ass guy making sure the suspension hugs the pavement :D

Assuming Cd = 0.47, frontal area = 25.5 (from smokemup.com), drivetrain losses at 25%, and the power curve we came up with on desktop dyno:

You can make 150 in 3rd at 6000 with power to spare. When you hit OD, your rpms will drop into the 4's, and you won't pull past 160. If you had a rear end ratio of roughly 4.3, I think you'd hit 174 at 6100.

If you drop your Cd to 0.42 (which is what smokemup shows) and go to 4.11's, then you should be knocking at the door of 180 at 6000.

All of this is of course sensitive to your final Cd and frontal area, but it seems like your gearing is your limit to speed

[Fuelie Fan]

It's deceptive becuase of the overdrive. 4.11's with a 0.7 OD (700R or 4l60e) is the same as running 2.88's without any OD (350 or 400 turbo), so it's not as much gear as it seems at first glance, though still uncomfortable at 75mph cruising. By comparison, 3.42's through that 0.7 is like running a 2.39 rear and no OD, which is so steep that it should be no suprise that's hard to pull to top speed.

I'd agree with you, 160 is plenty, and I wouldn't sacrifice the highway cruise RPM's for a little more top speed, considering how this vehicle will be used. with the 3.42's, 70 mph will be a sweet 2000 rpm's. With 4.11s, 2000 is only 60mph.

For those who WANT maximum top speed, despite the appearance of the equations above, it's not too bad, but you have to have good info to start with:

Step one: Find out how much power you have at your rear wheels, and at what RPM it occurs. Dyno, estimate, whatever. It must be rear wheel estimate though.
Step two: Figure out or estimate what your Cd and frontal area are
Step three: plug those values into the simplified equation
V = [(P*139120)/(Cd*A)]^1/3
to get the maximum speed possible considering your available power from step 1.

NOTE: This only works at sea level and with area in Ft^2 and P in hp, you'd have to revert to the full equations above if you want to change elevation (and hence density) or units.

Step Four: Figure you gearing so that your engine is spinning at the max power RPM in the desired gear when the vehicle is moving at the max speed.

[Marcus SC&C]

All that math is very impressive looking but it doesn`t explain why vintage NASCAR cars that were bigger and less aerodynamic than Chevelles were going faster than that with less power 30 years ago. Maybe it`s because those good ol boys didn`t know the math said they couldn`t do it? ;) Marcus

[Fuelie Fan]

ummm...because they were either smaller, more aerodynamic, or had more power to the ground than you realize? It's not like the drag equation is unproven:

http://www.lerc.nasa.gov/WWW/K-12/cd...ne/drageq.html