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

[jakobnev]

Could you post a wiring diagram?

Normally alternator output can be suppressed by boosting the voltage that goes to the sense terminal.

[MetroMPG]

^ True. That's what Daox did in this project: A better alternator delete



I was looking for a simpler approach that didn't require an additional power source/voltage booster.



I think I'm just going to put a big disconnect on the positive output wire. I've done that before with my Firefly which also has a "1-wire" alternator.

[GJKH]

Excellent, best fuel economy I ever heard of in a Miata. The best I returned in my 1991 was 36 mpg. Not bad, considering the gearing.

[California98Civic]

Originally Posted by GJKH

Excellent, best fuel economy I ever heard of in a Miata. The best I returned in my 1991 was 36 mpg. Not bad, considering the gearing.

MetroMPG is one of the masters of the mod and hypermile game. I would bet he could get quite a lot more out of this with more determination, but the driving would have to be ... different. I like Miatas, but what is incredible about your '92 VX is that it has been getting MPG in the 54 mpg without hypermiling but just driving posted speeds, running the car as engineered from the factory. The VX is a legend.

[GJKH]

Originally Posted by California98Civic

what is incredible about your '92 VX is that it has been getting MPG in the 54 mpg without hypermiling but just driving posted speeds, running the car as engineered from the factory. The VX is a legend.

Wow, you are getting 66 mpg in your 98 DX lately. Fantastic.

So far I am averaging 42 mpg in my 2000 LX manual tranny. Hope to do better, but happy with it so far. This is not hypermiling btw, just driving conservatively and driving as a "momentum car" (learned that years ago with the diesel rabbit),

[California98Civic]

Originally Posted by GJKH

Wow, you are getting 66 mpg in your 98 DX lately. Fantastic.

So far I am averaging 42 mpg in my 2000 LX manual tranny. Hope to do better, but happy with it so far. This is not hypermiling btw, just driving conservatively and driving as a "momentum car" (learned that years ago with the diesel rabbit),

Such capable little machines these cars are. That LX is basically my car with two more doors and some Lux Features and some chrome trim. You have the same D16Y7 engine and the same 5-speed transmission ratios. Before I knew what "hypermiling" is regularly got something like 33 or 36 mpg in combined city/highway driving because I did a number of hypermiling techniques instinctively as a game. Once, on a nearly all highway trip, I got 44 mpg on a tank (driving pretty slow and steady in the right lane). I have been driving this car for 20 years.

Peak of Honda's Cold War era engineering and manufacturing playing out, is what these late d-series Civics are.

[GJKH]

The 42 mpg has been mainly highway driving, 80%+. And I do drive for fuel economy, but I'm not a hypermiler. If traffic is light on the freeway, I'll stay and the right lane and go 65 mph, for example.

[MetroMPG]

52.9 MPG on the latest fill.

And that's the car's first complete fill of 2021. (Unfortunately, August was de-railed by a family emergency, so I haven't been using the car much.)

Originally Posted by GJKH

Excellent, best fuel economy I ever heard of in a Miata. The best I returned in my 1991 was 36 mpg. Not bad, considering the gearing.

Thanks!


Yeah, the gearing is atrocious for MPG. Great fun for accelerating / shifting, though. It's almost criminal to skip shift this car.

Anyway, I'm already running larger than stock wheels/tires on the back to address gearing, but I'm on the lookout for an even slightly larger set. I have a couple of friends with Priuses - the ones with 195/65R15 Ecopias. When they're ready to replace them, I'll snag some used ones.

[MetroMPG]

Filled up yesterday @ 53.5 MPG = 4.4 L/100 km.

That includes a modest amount of alternator-optional motoring in the tank. Maybe 15% of the total.

As usual, this was mostly in near perfect conditions on near deserted back roads, cruising at low average speeds. (Max posted limits of 70-80 km/h = 43-50 mph). No P&G, but plenty of engine-off coasting down hills & towards stops & turns. Top down 95% of the time.

I also changed the oil again. I had just done it in August, but I took things too far in terms of low viscosity -- I was hearing quite a bit of valvetrain rattle on start-up. 0w20 (what the Mirage uses) is too thin for an old Miata.

[MetroMPG]

MPGiata is back in hibernation.

I put about 2500 km on it this year. ~1500 mi.

Odometer passed 230,000 km on the current tank. ~143k mi.

The only new ecomod I did to it this year was to add an electrical disconnect to the alternator circuit.