Originally Posted by Kingtal0n

Did you not read: "modern EFI engine" a 1985 is not a modern EFI engine. V8's from pre-95 era tend to be sloppy and have reduced fuel economy and increased emmisions because of it. once you hit 1995+ especially 1998 era things got much better for V8's.

A 1998 LSx engine in a Miata should do 30+ mpg easily.
And weights are subjective. most 240sx start around 3000lbs, usually less. Sometimes as low as 2600lbs. A 2j only adds a hundred or two or three to that, usually 3200lbs or less is the final weight.
But we can gut and tube it to get it lower.