"MPGiata" modding thread: aiming for 50 MPG with a 1990 Miata. Update: success, 55 MPG!

[MetroMPG]

No brake return springs.



And, crud! My calipers look nothing like the one in that picture. The little holes in my brake pads that would take the spring ends seem buried too deep under the caliper to work. I'll have to see an OEM spring to be sure.


Mold ground zero??

I think I may have found the source of the mold!



I had put the plastic sheet in the trunk (the one I use to cover my leaky convertible top when parked in the rain)... and I put it away wet! Idiot!! The trunk carpet is stinky and has a real science experiment look to it.

[teoman]

https://m.youtube.com/watch?vl=en&v=NnFQy49mank

Maybe this can help waterproof your roof.

[MetroMPG]

So, I did a little (70 km) trip this weekend in great weather conditions (minimal wind) on a very MPG-friendly scenic route: 80 km/h / 50 mph max limit, through a couple of little villages with lower limits. Included several long engine-off coasting opportunities towards stops/turns...

• There: 52 mpg US (4.5 L/100 km)
• Back: 56 mpg / 4.2

Not too shabby! But it needs more mods. I'd like to be able to cruise at 50 mph at 50 mpg instant, and it's not quite there yet.

For comparison, here's what the Metro was doing on the same route in the same conditions (repeated on multiple trips)...

• There: 73 mpg US (3.2 L/100 km)
• Back: 78 mpg / 3.0

And I drove the Metro a bit faster than the MPGiata, and didn't have to concentrate as hard. Miata is a pig!

[MetroMPG]

Originally Posted by teoman

https://m.youtube.com/watch?vl=en&v=NnFQy49mank

Maybe this can help waterproof your roof.

Neat idea!


The top has lots of cracks in it. Needs duct tape or silicone sealant.

[MetroMPG]

Miata-owning buddy loaned me this to try out. A cursory search on whether/how it affects aero didn't turn up anything.



I know I said I wasn't going to do any projects to the car this year, but ... tuft testing to come.

[Stubby79]

Been meaning to mention it...I recently used "CLR" to get rid of mold on vinyl (motorcycle seat). Used it full strength, sprayed on, scrubbed and rinsed it off 15 minutes later...not even the slightest mark left behind from the mold.

[ProDigit]

Thought of water injection?

It would work well on this low compression engine.
You could also try to change to a thinner head gasket, in an effort to increase compression.

I wonder if there are many options for increasing compression ratio via the spark plug.
Like, if you could add mass to the spark plug, by welding metal to it, you're essentially increasing the compression ratio.

Hot air intake.

Check to see if there are aftermarket final gear ratio gears for sale (I doubt it).

Since the Miata is a rear wheel drive, you could see if you could take out the wheel well liner, and just coat it with some sort of protective paint; or even plastidip would work well. It would give you 1/2" to 1" extra to work with, to increase rear tire diameter.
I would also increase front tire diameter by a little, just not to create too much down force.

Another thing you can do, is decrease the width of the tires.
Get thinner, larger diameter rims. At least 1" larger in diameter, 2" preferred, and you should be able to cut 1" off the width (or more). Less wider tires mean less friction and road drag.
Thin profile tires usually are cheaper, and more fuel efficient as well. So you'll definitely need the larger rims.

[MetroMPG]

I have actually done some of the things you suggested:


- bigger diameter rear tires to reduce cruising RPM
- narrower LRR front tires


I should get on the warm air intake, though. That should be pretty easy.


I wonder about shaved head/thinner head gasket: wouldn't that slightly change the valve timing? Good or bad?



====


Latest mod: I did a tape measure DIY alignment this evening and set the front to zero toe. It was slightly toed-in.


I'm taking it on its longest yet voyage this weekend (400 km round trip). Thoughts and prayers, please! I'm trying to decide which tools to bring, just in case, without overdoing it (weight penalty). I'll be sticking the spare tire & jack back in.

[ProDigit]

It wouldn't change anything. More than likely the timing is too retarded anyway.
Should you run into any timing issues with 87 Oct, you could try running E15 fuel.


Do Piston coating, or replace the pistons with ones that allow higher compression.

[MetroMPG]

But none of those suggestions can be accomplished with duct tape!