Don Terrill’s Speed-Talk

Don't know if this will be useful, but here's the proving ground data for the '60 Valiant:

force required = 0.0246 S^2 + 0.317 S + 47.2 pounds

where "S" is speed in miles per hour.

A value of 0.454 was measured for the drag coefficient.

Manufacturers consider this information confidential for recently produced cars.

Another factor that i wonder about is what about the car that never settles downtrack and holds the nose up, even through the traps. I guess one could film it from the side to get an idea of how high the front fender is compared to static height while not under power. I'm sure there is a way to get the car to settle better and improve top end speed.

hsutton wrote:Another factor that i wonder about is what about the car that never settles downtrack and holds the nose up, even through the traps. I guess one could film it from the side to get an idea of how high the front fender is compared to static height while not under power. I'm sure there is a way to get the car to settle better and improve top end speed.

You raise a very interesting point. For more than a few years we have obtained the airfoil shapes of wings used on race cars, plotted their points in a cad program and entered them into an aerodynamic analysis program.

The program computed (and displayed) the aero slipstreams, local pressure vortices, separation points, but most important it calculated the drag and lift forces at any speed and Reynolds number.

We have been considering doing the same thing with the shape of a car. It could be run at various attack angles to determine the drag and lift forces that affect the car. Aero lift must impact rear wheel traction.

hsutton wrote:Another factor that i wonder about is what about the car that never settles downtrack and holds the nose up, even through the traps. I guess one could film it from the side to get an idea of how high the front fender is compared to static height while not under power. I'm sure there is a way to get the car to settle better and improve top end speed.

I would think the best approach would be what Nascar does or a solution along those lines. They use bump stops, soft springs and a sealed engine bay with the right kind of shape on the nose to wheel well area to suck out all the air. I have heard they get over 400 lbs of down force from this.

I did have a wild idea about trying a stacked double spring on the front coil overs. If you use two different rate springs the total spring rate is less that the lowest rated spring. Once the lesser rate spring binds the rate reverts to the highest rate spring. If this was with the nose just above the ground, it wouldn't be all that bad. I have never tried this but feel free to tinker with it. The Dirt Late model guys use the stacked spring on the left rears at times. A thought about the venturi effect on the engine bay from the wheel openings. It could be achieved like the Le Mans type cars and vent threw louvers at the front top of the fender. There are way too many to be just for brake cooling, and they could have gotten that from ducting.
the big trick would be finding that low pressure area with out a wind tunnel.

Variable rate spring? Saw them somewhere....

jacksoni wrote:My third gen (86) firebird is 21.4 sqft. ( have measured it ). Generally you can get pretty good estimate taking widthxheightx0.85. Taking of mirrors, getting it low, blocking off flow through grill/radiator (if legal), keeping air from under the car etc can go long way it improving Aero Drag.

This model Firebird is probably the most aerodynamic of all the "f" bodies built by G.M. It is even more slippery than the gen 4 cars. The C-5 corvette is more aerodynamic and would probably be faster if one could afford to build one. To Larry Meaux; there is a racer from NMCA that decided to go back to an old '70 Chevelle to take advantage of a 75 lb. weight reduction offered for the nostalgia bodies in order to make the competition closer. He has a post over on Yellow Bullet i think about the results. Even though the Chevelle only had to weigh in at 3475 it was 13 hundreths and 5 MPH slower than the '99 Camaro at 3550 lbs. with the same drivetrain. The Chevelle even had a better sixty foot of 1.26 vs. 1.28 for the Camaro. The engine was a 525 cu. in. BBC with a dynoed 1036 H.P. but i don't know what the rest of the drivetrain consisted of. The Camaro ran 8.90 @ 152.80 while the Chevelle could not run quicker than 9.03 @ 147.80 with everything else the same. After a reworking of the heads by someone who was good it later ran over 153 MPH somewhere in the 8.70s, but had an additional 100+ H.P. He's looking for another late model Camaro now.

David Redszus wrote: ↑Wed Nov 28, 2007 9:25 am For anyone really interested in determining the Cd and rolling resistance of their car, send me an email and I'll send an excel program that will calculate Cd, rolling resistance and power required (at any speed).

David,
I am just a few years late. Can you email me a copy?

Thanks,
Stan