Assuming you picked a diesel car that had similar power and performance specs (they had a Mercedes at 700 hp) I doubt what you say is true. Sure if you compare it to a 100 hp Jetta, you may be right. But that is an unfair comparison. That is like saying a F-18 will always be faster than a Cessna 150. It is a true statement but means nothing. Unfair comparison.
Ha... good comparison...
I was going to do the following in real life and not just for cannonballing...
Good aero can make up for a large difference in HP...
1) I have already done grill blocks out of clear polycarbinate (seems to help with aero big time since my MPGs have been increased measureably .... theory : pointy front end cuts the wind better (think plymouth superbird although not that extreme obviously).
2) I have yet to do mainly because I don't have a lift but was going to eventually .... smooth belly pan .... eco modder has a few examples of this on a Jetta ... my inspiration!
3) Kamm Back .... I am now debating on whether I should use the cardboard from my new RSB to mock up a fuel tank or the Kamm back .... I'm guessing Kamm since the fuel tank idea is more theoretical than an actual will do project (I use the car daily and having a 60 gallon tank inside takes up valuable cargo area more than you would imagine .... Of course if we really do run it it would only be a temporary install none the less .... I'm guessing 500 lbs should sit fairly still without a whole lot of tie downs ....
Just Kidding of course! ;-)
Kamm would be made form clear polycarb so as to be somewhat stealthy and not impair rear vision ...
3) Side skirts may or may not be needed with a belly pan smoothing the undercarriage.
4) I am planning on removing the roof racks when the upholstery shop does the sagging headliner (I'll wait until it warms up a bit because I will sound deaden the roof while its apart too).
5) I am installing better / more inside mirrors and effectively eliminate the outside mirrors (will keep nominal 2" small convex outside mirrors on custom mounts to pass state inspections (in VA outside mirrors have to let you see 300 feet behind the vehicle .... I figure if I can see the sky that's plenty far away!).
6) Have to investigate wheel spats more ....
7) Maybe fill in / cover rear wheel opening
8) May get large enough magnetic sigh material to cover door handles (not quite shaved but I guess better than none).
9) Still have not done the pizza pan wheel covers ..... yet
Anyways, better aero would help get higher top end speed and when driving normally should help MPG's big time ....
10) rear diffuser
Any other aero ideas I have not though of ?