[jeffcat]

I'm sure it can be done but gearing is your biggest enemy. You are going to be cruising at really high RPMs because it's geared so short. Your best bet is a larger overall diameter tire to change the gearing and get the RPMs down. Obviously make sure the air vane or maf is all up to snuff. The engine doesn't do bad...it's just geared extremely short for obvious reasons. The 323 had the same 1.6 and got 37mpg.

The miata is God awful in terms of aero. The hardtop has the least drag. Also put an R style front lip in the front bumper as an air dam. Around the rear bumper you need an underbody tray because the bumper cover acts like a parachute. The whole underbody could use a tray to be honest. Then you could go for narrower wheels if you have some or put some racing style fender flares on it to enclose the wheels better.