Coleman Autosports: 24 Hours of Lemons Racecar

The Car

1985 Mustang GT
302 with aluminum intake and Holly 4160 4brl
5 speed manual
3.08 rear end with re-stacked and shimmed Trac-Loc for higher TBR
Unsprung rear wing with over 400 lbs downforce at 100 mph
Front splitter and airdam with brake cooling ducts
10 point roll cage
Upgraded brakes
Trimmed coils with performance alignment

Wing and Splitter Testing at TWS

Chasing a Spec Miata

(Click Youtube link in video to view in higher resolution)

First Lemons Race
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We are car #1 when the green flag drops and I begin lapping the field after one clean lap.

Track Testing

Porsche club track day at TWS

I was only hitting 119 mph and the Porches would pass me at over 140 mph on the high bank. But once on the road course I could reel them back in and occasionally pick one off.

Wing Design

It was decided to increase the cars performance we should investigate an Aero package. However, at the low speeds encountered at a typical Lemons race (less than 100 mph), a wing with a high CL would be necessary to get adequate gains to justify the added weight and considerable effort.

A 6 ft wide double element WORTMANN FX 72-MS-150A AIRFOIL profile was selected based on the availability of wing data for modeling, the high coefficient of lift, and the modest drag at the low speeds encountered at Lemons races.

During the wing design process a spreadsheet was developed to quickly associate numbers to the various wing designs. The spreadsheet iterates through different speeds and calculates the downforce and drag for the wing at speeds from 30-120 mph. The calculation is based on a coefficient of lift and drag for a double element WORTMANN FX 72-MS-150A AIRFOIL at a specific angle of attack for standard temperature and pressure. A range of 0-15 degrees to the relative wind was evaluated with 5-10 degrees being optimum from the wind data tables.

Over 400 lbs of downforce at 100 mph!

Just don't go much over 100 mph because the wing exponentially turns into a parachute
and most of the Mustang's ponies ran away in the early 1990's.

Many thanks to my buddy Brian for running a few CFD scenarios on the wing to see how well the computer agrees with our assumptions. The next step will be a laser scan of the car to create a mesh. We will then be able to see how the airflow from the car is affecting the relative wind to the wing and make changes in the computer to optimize wing height and angle of attack.

• Base (15 Degrees)

– Down Force = 583 lbs

– Drag = 113 lbs

• +10 Degrees (25 Degrees)

– Down Force = 441 lbs

– Drag = 132 lbs.

• -10 Degrees (5 Degrees)

– Down Force = 670 lbs

– Drag = 140 lbs.

• +5 Degrees (20 Degrees)

– Down Force = 525 lbs

– Drag = 127 lbs.

• -5 Degrees (10 Degrees)

– Down Force = 618lbs –Drag = 109 lbs.

What do I do with 500 lbs of downforce?

Well it turns out that 500 lbs of downforce into the rear of a fox body mustang will put the measly 200 lb/in rear springs into the jounce bumpers and make for a very difficult to control Lemons racer. Especially over curbing at high speed. So.....we took a page from the Chaparral Can-Am racing cars and designed an unsprung rear wing.

All downforce goes directly to rod ends mounted to the rear axle, thereby channeling all force directly to the tires. The mounting points for the links to react the drag forces had to be chosen carefully to maintain proper kinematics in bump and roll and to keep the wing from moving longitudinally in bump.