I've had my 85 2M4 for nearly a year now, and I've been thinking about engine swaps for a while. It's definitely not something I can start immediately, but I want to have a good idea of what I'm looking for so that I can start working in that direction.
When considering what I'd be looking for in a swap, I have a few criteria: firstly, I really like that my car gets good gas mileage, and I'm not willing to sacrifice that on the altar of more horsepower and lower 0-60 mph times; secondly, I want to have a reasonable amount of space to work in the engine bay, if possible, because I don't want maintenance to turn into a nightmare; thirdly, my car currently sports the 3-speed auto that is completely terrible, so in the event of a swap, it needs to go. Based on that, I definitely want to stick with a I4, though I would be willing to consider a small six-cylinder, and it doesn't necessarily need to be compatible with a stock transmission (though I would consider dropping in the 5-speed stick and hooking it up to a decent, compatible four-pot if one exists). I'd also like to upgrade the brakes and suspension, so if I would consider doing a custom setup for the new engine/trans combo.
The 2.0 L MZR from the first-gen Mazda3 caught my eye as a potential swap. Of course, that's purely theoretical because I can't find anyone who's done that swap and I am not familiar enough with the engine to know the plausibility of putting it into my car. However, it's an engine that I believe meets my criteria fairly well.
I would love some input, because at this point I'm just an amateur bouncing ideas around in my head that don't have much grounding in knowledge and experience.