[Honda100]

I just want to chip is as I actually own a lean burn Toyota and also someone who has swapped motors before. I have a 99 Corona Premio E with an automatic.

First off, I don't get anything near 50 mpg us. In fact, sadly to say I haven't even broken 40 yet. Personal best is 38.9 and I average around 33. Japan's fuel mileage rating system is worse than the EPA's by a mile. It bases cruise speeds at a MAXIMUM of 44 mph, so anything resembling freeway speeds that Americans are used to will decimate the fuel mileage.

Secondly, you can't just swap the intake manifold and ECU, you need at least the harness for the manifold and then need to pray that the wires themselves are not shielded in such a way that you can't splice it together. If that's the case, you'll need the entire harness for the engine (remember the J-spec ECU probably wont be able to interface with the US versions of the cooling fan relays, mass air flow sensor, coolant temp sensors, etc). So, at least you'd need all of the relevant sensors to go with the intake manifold, and likely all of the other sensors as well and the accompanying wiring harness as well. In short, it's not plug and play and from the actual fuel mileage standpoint, not worth it either.

Since you don't have emissions where you live, I'd just get a standalone ECU, rebuild the motor with a higher compression ratio, run it on premium, advance the timing and run it as lean as it'll go. I have a Nissan 180sx that I swapped a non turbo motor in from a 240sx and that's exactly what I did, except that I added a 3 inch radiator for cooling. The EPA rates the 240sx at 21 mpg and I am touching 30 at almost every fill up and have almost 170 horsepower at the wheels. Might be something to consider.

Good luck