Every time I look at Andrew's air dam I think the same thing... "it must be too big!".
But his coastdown testing shows a significant improvement.
The air dam is similar in size to the one on Car and Driver's crisis-fighter Pinto, which they measured as worth a 6.25% increase in MPG at 70 mph. It's equally as massive, with only 2 inches of ground clearance (which must be well below the lowest hanging underbody components):
