[Apex]

Hey there guys!

Long time member, but I hadn't even realized I've never posted! First post!

I drive a 1990 Mazda Miata. The stock 1.6 is getting tired, but not dead yet. I was going to take advantage of the situation and take my time rebuilding a cheap used 1.6 and swap it in when I'm done, but my opinion has recently been changed and I've decided it's probably best to swap in a 1.8 from a later model, maybe with VVT.

Though I'm having a bit of trouble with the decision because while the gearing of the Miata isn't ideal for economy, the 1.6 sips fuel at such a rate that I can still get nearly 40mpg cruising! The 1.8 on the other hand, in stock form, struggles to get 30 at speed...

I'd like to get more power out of whatever I swap, but I don't have very ambitious goals (150-170hp at the wheels) -- I'm pondering what kind of modifications I can do that will net me more mpg. Strictly speaking about the engine here.

My best guesses:
High Compression
Turbo (though I'd like to keep the build N/A and possible introduce an ITB and custom plenum/airbox setup)
????

Things I already have planned:
Aeromods including an undertray and signigicant trimming of the rear bumper
Differential swap to a tall australia-only mx5 turbo diff
Changes to wheel sizing