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

[freebeard]

Bellmouth the radiator inlet.

The weight reduction and reduced inlet should be good for 0.1mpg. You'll have to adjust your goals upward.

[Stubby79]

Metro, you sure do fill up a lot. Just how far are you going between fill-ups? and how is this going to mess with accuracy?

(I have taken to only believing a full tank worth...sure, I could make a single trip that might get 60mpg, but over-all I would only see 40 for that tank. That's too much like stacking the cards in my favor, just to see the results I want)

[MetroMPG]

Stubby: FYI, the car's fuel log is up to date.

Some have been short fills of a few hundred KM (smallest fill a result of wanting a "reset" so I could calibrate the newly installed MPGuino from full).

All my fills this year have been at the same pump, and I top it off completely (until I see fuel in the filler neck).

I'm pretty confident in the numbers.

[MetroMPG]

Originally Posted by freebeard

Bellmouth the radiator inlet.

I actually kind of did that: it's a rectangular opening, but the edges are radiused (maybe r = 1").

Also: radiator efficiency is noticeably improved with the AC condensor out of the way! I need an adjustable grille block.

[MetroMPG]

Originally Posted by kurzer

i learned in this time, that the OL is very, very rich, so i´m not suprised by your warm-up observation.

Done! Easy modification. Thanks again.

My exhaust pipe is definitely very sooty. Running rich? Or just an old pipe with years of accumulation?

The exhaust gas analysis is the best method to confirm - that will be next year's e-test for me.

Tomorrow morning's "cold" start (~15C / 50 F) will determine if the adjustment (4 clicks) will affect open loop driveability.

[MetroMPG]

Next mod?

[Stubby79]

Originally Posted by MetroMPG

Stubby: FYI, the car's fuel log is up to date.

Some have been short fills of a few hundred KM (smallest fill a result of wanting a "reset" so I could calibrate the newly installed MPGuino from full).

All my fills this year have been at the same pump, and I top it off completely (until I see fuel in the filler neck, just above the flap).

I'm pretty confident in the numbers.

ahh, wel;l...it looked liked you had filled up two or three times inside of 2 days with your reporting your MPGs....or is that off of your MPGuino?

[freebeard]

Off to a good start. What do you think about follows the side trim line forward to the door and then straight down?

[AdrianD]

Props to you OP for having the composure to drive steadily and economically. I can't do that in my Miata

Regarding differentials and gearing, I installed a 3.9 differential in mine, while it originally came with a 4.1 (94 model, with the 1.8). The new diff is off a 10th anniversary NB model. The rev difference is not a lot but it makes for a tad quieter ride. In town however I used to drive almost everywhere in 5th gear, now I only use 5th above 40mph as if feels that I'm lugging the engine.

If you could live without having the top down, you could invest in a hardtop plus a hardtop spoiler. The hardtop spoilers for the Miata seem to continue the slope of the hardtop nicely for aerodynamics.

Later edit:
About the soot on the tailpipe, as far as I know Miatas are tuned rich from the factory. If you want to get that out of the way, take a look at Speeduino, open source ECU. Cheap, already available with plugs for the Miata wiring harness and tunable with the same software as Megasquirt.

You can also increase timing by rotating the cam angle sensor and see how that helps your mileage.

[Baltothewolf]

Oh yea I forgot about adjusting timing! Definitely do this. Bump it to 12°. You can still run 87 (whatever the cheapest is) without pinging and it gives you about 5% economy.