[fujioko]

I built two + 40 MPG Miata's.

The first one had a three cylinder geo metro engine. The G10 engine didn't have a lot of low end power.

My second Miata has a B3 1300 engine from a Festiva, This is a great engine and it delivers more than enough torque on the low end. The B3 version is an excellent overall performer for daily driving. The only negative is the B3 falls flat on its face above 4200 RPM.

An untested alternative to a motor swap would be...

Start out with a 1.6 first gen Miata. Swap in camshafts from an automatic equipped Miata. This will bump the TQ up and cut the HP a little.

Next, swap in a RX-7 fifth gear set.

Finally swap out the 4.30 rear axle with a 3.90.

I have no idea what to expect with that combo but it should be a good start.