Swap Insight 1.3 engine with 1.0 engine
 

- the stock engine is 1.3 and four cylinders
- the spare engine is 1.0 and three cylinders (from a wrecked insight)

Does this seem like a doable mission? Or better-off just leaving things as they are (no engine swaps)? I estimate fuel savings would only be 10 mpg. About 0.1 gallons saved per 100 miles (33 cents saved/100 miles).

10mpg sounds good to me.

Likewise. Depending on how much you drive it could be very worth it!

EDIT: Of course I say this without knowing your expertise, OR even what would be involved with the process and how much it would cost...

Are you going for extreme fuel economy, or tring to save money? At the rate of 33cents per 100miles you suggest, that's over 150k mi to save $500. Is the engine and labor to swap free?

I'd say no.
Most of the time I drive with the CVT maxed out in 'top gear', and then it ticks over at just under 1000 rpm per 30 mph, EGR valve open at 30%, engine load at 60% or so.
Pretty much maxed out efficiency wise.
I believe the G1 CVT revs higher per mph? And that was designed for a lighter car with smaller wheels.

Also, you'd need a G2 with engine trouble as a donor car if you don't want to waste money. That is a rare beast though.

There are so many cars around with much bigger engines than a G2 Insight that could benefit much more from having smaller engines. Why the Insight?

A better idea would be to take a gen 1 and install a diesel engine from a generator and hope the ima can be reused, but if not between the weight savings and efficiency of a diesel engine you should easily get over triple digit mpg.

I wonder, can the hybrid electronics from the G2 power the G1's electric motor?

Probably not economical, but academically interesting.

Im sure it can, its a 3 phase dc motor. Just hook up the rotor position sensors and the 3 orange cables. Another option if you got a power source and the "speed controller" from the ima system and rotor position sensors hooked up you just need a square wave generator to signal it.

The engine will not like the extra 750-800lbs and added frontal area. The gen 1 is a slow poke, which is fine, but climbing hills and mountain passes with a Gen 2 body would give you a lot of anxiety. Not to mention the rolling resistance from non oem tires.

A turbo might help. I met a guy with one on a gen 1, and he said 5lbs of boost max is the safest.

I wouldn't quite say it's a slowpoke, but if you don't want it to be, you will spend a lot of time in 2nd, 3rd, and 4th. With the extra weight &c, and a CVT that's probably not adjusted for it, you'll probably not see that much advantage.

FWIW, my Gen 1's fuel consumption takes a significant jump when the VTEC kicks in at a bit over 3K RPM. If you have to spend most of your time above that to move your Gen 2, I'm guessing that you'll likely not see much advantage. At some point, it boils down to the fact that it takes X amount of energy to move the car, and if you can only get that output by running the smaller engine outside its best BSFC area, it won't improve things.