I had a 1990 Miata, 1.6L / 5-speed / AC and could get 36 to 38 without engine off coasting on my gentle commute. I got 26 MPG the {only} day I autocrossed it. It was a blast to drive, but I wanted more. Mods to that car: low profile headlight conversion (cuts the open height in half, dramatically better light at night), cold air intake, converted to a Camaro single in dual outlet muffler because I wanted dual exhaust out the back (too loud / too large an i.d. for only 1.6L). I got 38 MPG on the interstate returning from a trip from Deals Gap (had to run the Dragon
) and when I mentioned fuel economy at the next Miata Club meeting I was told by the Chapter President that if I was concerned about fuel economy, I was in the wrong club.
Have fun, I'm certain that 40 is doable in a 1.6L Miata.
