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Old 08-27-2014, 08:11 PM   #1 (permalink)
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Performance oriented mod -- can I still get better mpg?

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

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Old 08-27-2014, 08:14 PM   #2 (permalink)
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In my experience, the BP engine takes much better to a turbo build than a NA build. You can always size the turbo to keep out of boost at "normal driving" RPM.
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Old 08-31-2014, 02:19 AM   #3 (permalink)
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Quote:
Originally Posted by bhazard View Post
In my experience, the BP engine takes much better to a turbo build than a NA build. You can always size the turbo to keep out of boost at "normal driving" RPM.
Totally didn't notice someone replied to this!

That's what I've heard -- actually that the 1.6 prefers a little bit of FI as well, but it doesn't really sway me.

I'm looking to keep or add as much peppiness to the engine as possible and I'm not concerned with huge power gains.

While a turbo would be a good way to use otherwise wasted energy, it just isn't what I'm interested in for the car (I'm not anti-turbo! I promise!). The Miata as a whole package just has so much potential to be a FUN hypermiler but it also has so many things working against that. When it comes to Aero and Gearing I already have plans, which I've mentioned, but there's not too much more I can do in those departments.

That brings me to the engine. We know it's not INEFFICIENT but there's got to be a few things I can do to bring up those MPGs!

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