CD and Frontal area?

[tminer]

Does anybody have approximate Coefficient of Drag and frontal area numbers for an 87 GN?

Generic values for all TTypes would be OK, or if you have specifics by model I can use them all.

I need the info so that Lockers can calculate HP and TQ.

Thanks,
Tom

 

[UNGN]

Use the GN Specs 3 view to determine frontal area.

Determine the scale of the drawing using the known width and height of the car, then draw a scale 12" grid over the front view. Count up the boxes and partial boxes. This is a rough approximation of the cars Frontal Area in square feet.

Assume the Cd is around .38-.40 which is approximately twice the coefficient of drag of an unladen African swallow.

You can also determine aero drag by using car and drivers calculated coast down road HP numbers in the performance section of the specs.

Road HP = Aero HP + mechanical Friction HP

Assume Mechanical Friction HP to be a constant (though it isn't really)

30 MPH = 7 HP
50 MPH = 17 HP
70 MPH = 37 HP

And subtracting out 6 HP for mechanical Friction we get

30 MPH = 1 HP to overcome aero Friction
50 MPH = 11 HP to overcome aero Friction
70 MPH = 31 HP to overcome aero Friction

Plugging CD and drag values into a web aero drag calculator (http://www.smokemup.com/auto_math/hp_wind_resistance.php) until the above values roughly match (give or take a few HP), I get:

100 MPH = 92 HP
130 MPH = 195 HP
160 MPH = 360 HP
190 MPH = 595 HP
200 MPH = 695 HP <= 100HP to go 10 mph faster...Yikes

 

[tminer]

Thanks!

Tom

 

[victa1]

I believe the CD of a GN/Regal is more like .45. Looking at that old Car and Driver report, it takes over ten seconds to go from 110 to 120 mph. And certainly, it would take more than 195 road HP to reach 130 mph.

I still have trouble believing that the bone stock '86/'87s, with the speed limiter removed, could do the 145-150 mph as some people have claimed. I would think that the aero drag above 135 or so would be too much for the available power at the wheels to overcome. The stockers really slow down above 110 or so.

The Corvettes of that time, with less frontal area and much less aero drag, could only do about 150 mph, and that took a very long
straight. Granted the blown 231 could put down a little more power at the wheels than the L98 Vette, but not enough to overcome the greater air resistance.

 

[UNGN]

Originally posted by victa1
I believe the CD of a GN/Regal is more like .45. Looking at that old Car and Driver report, it takes over ten seconds to go from 110 to 120 mph. And certainly, it would take more than 195 road HP to reach 130 mph.

That's because the car shifts into OD from 110-120 which isn't a "close ratio" shift. Given the cars stock fuel pump and the admitted "brutal cold temps" during the CD test, the car likely retarded big time on the 3-4 shift.

A stock GN will run 130 mph without too much trouble. The trouble comes from the front end lift from the intercooler scoop pressurizing the underside of the hood. This lift will increase the effective frontal area and Cd while making the car increasingly more unstable a speeds increase.

 

[troyk]

So do we have a final answer for his original question of frontal sq/ft & drag coef values?

 

[edfiero1]

I'd also be curious to know the Cd on the G bodys like the Monte Carlo SS and Grand Prix Aerocoupes. How much did that back glass help with the Cd ?
Anybody ever try that glass on a GN ?