This is the sort of thing which makes me really suspicious of Cd data measured and published by people who have vested interests, as most have through time:
Aerodynamics and Efficiency Through the Air – Honda Insight, Toyota Prius, and Chevy Volt :: Auto Upkeep Blog
I strongly suggest that we really don't know much about the precise Cd of many cars past the theoretical objects such as Lange's theoretical car. (Which I think I recall that Hucho verified with only slight difference.) Folks with vested interests produce biased results. Some of the data is too old and too unreliable and some of the data is pretty clearly biased. Chevy certainly doesn't have a very credible record when it comes to dishing out numbers. I trust Hucho's VW tunnel data, but any derivative data is questionable IMHO.
This is not to say that our reasonably proven techniques, such as the template, and tuft testing, and the obvious such as grill blocks and mirror removal won't get us better MPG, but we won't necessary know what Cd we started with and we won't know what Cd we gain.
Sorry for the rant, but I just can't contain myself when I see this sort of thing published.
