Cobra drag co-efficient....is it a "barn door"?

[xb-60]

Originally Posted by Dominik

....Fact is, the 427 has a very bad drag coefficient......+/- 570Hp (DIN) to get to 198mph in the late 60s....

But back to one of the earlier posts, it may have a seriously unimpressive Cd, but its frontal area is small, and that surely significantly negates the big Cd number?

[Silverback51]

Originally Posted by Dominik

I agree on various numbers for losses due to poor exhaust design, but one shouldn't add 80 - 100Hp as a default to rwHp just to make it sound good at the next bench racing session.

And I don't agree on the 20% losses for the drivetrain. Your transmission engineers would kill you for that bad percentage. Also, nobody rated a Nascar 750Hp 358cui at 1.000Hp just because the valve train and friction took away 250Hp at max rpm.

Fact is, the 427 has a very bad drag coefficient. We tested it in 1995 with GM's (OPEL) engineering team on the German A5 Frankfurt-Darmstadt (no speed limit).

+/- 570Hp (DIN) to get to 198mph in the late 60s? Very much achievable by Dick Smith's engine builder. What windshield did he use??

But we will never change this SAE/DIN debate :-)

It's more than just the transmission. I agree if it was a 20% loss in just the transmission due to resistance the transmission would get very hot.

It takes power to turn the transmission, and you also have to overcome the flow of the transmission fluid. That's why all modern transmissions use ATF fluid instead of the 90 weight gear oil they used to use. Same holds true for the rear end. Disk brakes drag and that takes power to over come. Axle bearings have resistance. It just goes on and on.

[ERA Chas]

Originally Posted by Dominik

Fact is, the 427 has a very bad drag coefficient. We tested it in 1995 with GM's (OPEL) engineering team on the German A5 Frankfurt-Darmstadt (no speed limit).

Could you post that data and details of the car/ test methods please?

[strictlypersonl]

If someone has an accelerometer, it should be possible to calculate the drag with only two speed readings (although more would be better). Take the deceleration values (with the car in neutral and coasting) at 100 mph and 40 mph, for instance. A little figuring can differentiate between the (constant) mechanical drag and the aerodynamic drag, which varies by the square of the speed.

[Dominik]

It has been done with an accelerometer on a know road (profile).

Yes: you accelerate, take reading. You decelerate (coast down) to get your baseline of resistance. From 120kph rolling resistance is small in comparison to aerodynamic drag.

We took 2 readings per front wheel revolution. OPEL tested their faster cars there too, like DTM and Lotus Omega.

My number look similar to the ones posted above. I pdf'd the Excel (one page) but the file size exceeds the limit. I try to send to ERA Chas.

I also aim to upload a pic here. It was a UK RAM with Hardtop, no side windows.
My passenger was very heavy, so we got 1.250kg as weight with the equipment.

Pics not working, I guess I can add them to my photo library?