[wmjinman]

Regarding that article in "Hot Rod" magazine, their goal was to break speed records at Bonneville Salt Flats (and they succeeded) They went to an actual wind tunnel to optimize their car. Did Mythbusters use a wind tunnel? Again, I didn't see that episode, so I apologize.

And in this case, at least, they speak the truth. The big flat air dam that looks like a "barn door" - I built one just like that for my car. In coast-down testing, I was able to confirm that it was better than either no air dam, or a more "conservative" air dam I also made. So for higher speeds (I did my coast-down testing from 105 mph to 65 mph), their air dam advice is correct.

As to lowering the car as far as you can, that seems to be correct, too. I also tested that using the same method (coast-down from 105 to 65) by compressing and/or shimming the coil springs. I had already lowered the car, but a friend thought raising the back some might help. His idea was to try to "dip" the nose a little by changing the car's overal angle & push more of the air over the hood & top, while reducing the air under the bottom. - didn't work. The "Hot Rod" article said, lower the car, both front AND back as much as you can. And I got the longest coast-down times by doing just that - putting the front and the back as low as I could get them.

Now, with the layer of foam on the hood and the roof, I think you will definitely get some insulation out of it, but I'd wonder about increasing total frontal area. You may be able to make up for that by carefully contouring the front & back to make the car's overall shape more "aero" - especially the back, if you extend it into a "Kamm-back" type deal. Hard to predict - that's probably one of those things that would have to be determined experimentally.

EDIT: Another reason my friend thought we should try changing the position to "nose down" was to help with "downforce". But it wasn't needed - the air dam did the job... up to over 180 mph, at least. We got the car over 175 on 3 or 4 runs, hitting 184 once. And that thing stayed plastered to the ground like you wouldn't believe. My friend said he could actually feel is "crouching down" as the speed went past 150-ish.