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

[Stubby79]

Originally Posted by AdrianD

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.

There's also the air-flow meter adjustment that will lean it out.

[Stubby79]

Originally Posted by AdrianD

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.

There's also the air-flow meter adjustment that will lean it out.

Oh and between my cleaning the ground connections and installing a heated O2 sensor, my tail pipe isn't quarter as sooty as it used to get.

[AdrianD]

Originally Posted by Stubby79

There's also the air-flow meter adjustment that will lean it out.

Oh and between my cleaning the ground connections and installing a heated O2 sensor, my tail pipe isn't quarter as sooty as it used to get.

I never knew about the air-flow meter adjustment. Could be different between the 1.8 and 1.6 models.

A new O2 sensor would definitely help.
There are reports of people who turbo Miatas and get better mileage if they keep out of boost, as the stock tune could be leaned out.

[Baltothewolf]

Originally Posted by AdrianD

I never knew about the air-flow meter adjustment. Could be different between the 1.8 and 1.6 models.

A new O2 sensor would definitely help.
There are reports of people who turbo Miatas and get better mileage if they keep out of boost, as the stock tune could be leaned out.

You can't adjust the AFM on the 1.8 cars, only the 1.6.

Heated o2 definitely helps. Worth doing, considering how cheap iit is.

Typical gains on a aftermarket ECU wkth a completely stock engine are 10%, sometimes as high as 15%.

[MetroMPG]

Yup: I've done the timing advance:



And as of yesterday afternoon, the airflow meter spring adjustment as well:



Going right now to see how it affects a cold start...

UPDATE: the car has always had a slight stumble/miss on cold starts that lasts 10-15 seconds (plug wires?). It was possibly slightly worse on this start-up, but not significantly. Could be my imagination. I'll leave the adjustment where it is.

[MetroMPG]

Originally Posted by AdrianD

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.

Even with just the taller rear tires, I've noticed I use 5th in town a little less than I used to.

If you could live without having the top down, you could invest in a hardtop plus a hardtop spoiler.

Heresy! I wouldn't have bought it at any price if it wasn't a convertible. There will be no more talk of fixed hard tops in this thread!

[Xist]

What if you got a really good deal?!

[kurzer]

Originally Posted by MetroMPG

the car has always had a slight stumble/miss on cold starts that lasts 10-15 seconds (plug wires?).

this is a common problem with miatas. the heat kills the plug wires, the plug wires kill the coil. dont use the old wires too long, 50.000-60.000km is the time to change.

[Baltothewolf]

Heat wrapping the headers helps a lot with the above statement, but you lose warm up efficiency so...

[freebeard]

There will be no more talk of fixed hard tops in this thread!

Carson-style aerocap?