I wanted to do a car that got near 50mpg, and it gets 45mpg currently doing 65-70 highway.
I put in a D15b Japanese engine with 35k after I blew the D16z for the second time, modified the aerodynamics, put on a refurbished cf hood, got rid of power steering and a/c, lightened the accessory pulley, and gutted the interior. I will get pics of the interior - the bare metal was all rhino lined, I made a custom fiberglass dash, and i put in an aluminum bomber seat.
It's a work in progress: it could easily hit 50mpg with some insight parts: gas tank, exhaust, rear brakes, etc.
i have video links on my facebook page which I will link below:
1) http://www.facebook.com/v/589369297369
2) http://www.facebook.com/v/589586297499
3) http://www.facebook.com/v/589590354369
Photo album of some of the build is here:
http://www.facebook.com/album.php?aid=2165012&id=32800953&l=0ee18fc3e0