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

[Dominik]

Yes, DIN and SAE came closer in the early 70s. But the typical hot rodder likes the "old" SAE. Now, let me get into this:

A rear wheel horsepower reading of 500Hp does not translate into:
500x1,2 (20% drivetrain loss) = 600Hp, plus 80Hp exhaust and accesory loss = 680Hp. Let make it 700...

It does translate into 550Hp DIN (in my car, most cars).

Sorry, to burst your bubble: There is no 20% drivetrain loss (in direct drive, 4th gear).
Just imagine 100Hp which is about 70 kiloWatt (240000Btu) which would be the same as 70 off 1.000Watt electrical heaters, or blow dryers.

Your transmission would almost be glowing red hot.

[Dwight]

In a conversation with Keith Craft I asked what was the hp loss for a Cobra. Keith said they saw typical a 20% loss. He dyno's his motors before they ship out. Sometimes he installs them into Cobra and then dyno's the Cobra.
Some of the CC members have dyno'ed their Cobras with different sidepipes and report losses of 40 to 100 hp.
I think Keith's experience is of value because he dyno'ed the same motor out of the car and installed.
I have hear loss numbers of 15% to 27% for a Cobra. But for most of us it's a guessing game. I had mine dyno'ed on a chassis dyno for rear wheel hp. I can only guess at the flywheel power.

Several of my buddies have motor that were dyno'ed before they were installed into their Cobras. They can only guess at their rear wheel hp.

Dwight

[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 :-)

[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?