Boy, I hate to admit to an advanced age, especially one that would allow me to remember this!
In 1975, during the infamous "gas Crisis", Car and Driver did some early testing of wind cheating devices to see what would enhance gas mileage. Their base test sled was a '75 Pinto 2300cc engine, with automatic transmission (more were sold than 5 speeds at the time, I believe). It was done on an instrumented car, at 75MPH, as I recall, on one of the southern Super Speedways...Talledega, perhaps?
Besides using headlight covers, blocking off the grill, then varying detrees of open, using an add-on rear spoiler, they also fabricated an air dam with wrap around edges, which extended down from the already vertical bumper.
Relative to the front air dam, the conclusions ran along these lines:
The LOWEST, deepest dam was the most effective. They began with a dam which was almost touching the pavement, and had to eventually trim the dam to allow for driveway clearance, only. Trimming was proved to diminish the effectiveness of the dam. I repeat: Lowest was the best.
Their explaination (theory, at the time?) was that the air drag from the additional frontal area was still less than the under-chassis drag from the "dirty" underside of the car. Cleaning up the underside (blocking off the air source) reduced the drag beyond the addition of drag from the increased frontal area.
Incidentally, the combination of devices they worked with (basic materials, with hand tools) gave and additional 25% boost in gas mileage.
I kept a copy of that article for years, as I was building a B Sedan Pinto, and copied their work. They then went on to evaluate various devices on a few other cars...I remember the Datsun Z car with commercial air dams used.
Not promoting any position here, only reporting what I remember of the article.
Good racing.
Bill
