My sugguestions
1.) The article says “Fiber glass”, I would change that to carbon fiber.

2.) Get rid of the neat looking rims, and use a cover that would make it a little bit more aerodynamic.

3.) Solar panels on the car to help with recharge.

4.) Get rid of the exterior mirrors and use camera – more aerodynamic advantage

5.) Bring the back further to make a smaller point.

6.) Make a “golf ball” pitted under carriage.

7.) Any part made of Iron or Steal that can be replace with a lighter material would be replaced. Aluminum, Titanium , etc..

The would what I would do first to increase my millage.

With regards to #2 would covering the wheels cause issues with brake cooling?

With regards to #7 carbon fiber can replace a lot of the steel in a vehicle. There is a question in my mind about safety. Steel will bend and twist in an impact. Carbon fiber will de-laminate and shatter. When properly designed both do well at converting the impact energy to heat before complete failure. However, in a non-racing environment I wonder about the real world efficacy of the carbon fiber to protect the occupants who are not wearing Nomex suits, helmets and 5 point harnesses. Bring on the crash test dummies I say!

Well, if he did it right – i didn’t see if he did do this – you would have a cage of some sort around the cab. The reason I said carbon fiber was to make it a tad bit lighter. Lighter car = less energy to move = MPG boost. Of course it’s probably a lot less of an MPG boost than it would take to justify the cost.

The XR3i was a slight improvement but the term XR3 still conjures up images of reverse baseball-hatted bad boyz.