Ecomodding 2015 MX-5 Miata

[Ecky]

EDIT: Updated. Car purchased!

The Insight found a new home, and I've moved overseas to New Zealand. Shortly after landing I picked this up:




Vehicle is a 2015 Mazda MX-5, which is not called a Miata anywhere but the US. I originally wanted the most basic base model, but made a call to get a few features (and some weight) I didn't care to have, in order to have a few others that were nice to have, at the same price. It has 56,000km (35,000 miles).

It's a Japanese import, and comes with an engine you can't get in the US - a 1.5L Skyactiv G engine, 129hp with a 14.0:1 compression ratio. It's hard to find the weight for this exact variant, but the base spec is officially 990kg (2180lbs) and best I can tell, this trim has ~20kg (44lbs) of extra "stuff". It's still around 108lbs less than the US base model.

Fuel economy ratings are:
30mpg City (7.8L/100)
48mpg Highway (4.9L/100)
39mpg Combined (6.0L/100)

Generally not relevant to fuel economy, but compared with the JDM base model, this has:
-Limited slip differential (vs open diff)
-Larger 280mm brakes front and rear (vs 258mm F / 254mm R)
-Alcantara interior (vs plastic)
-Recaro heated seats (vs cloth)
-Touchscreen (vs buttons and knobs)
-Bose 9 speaker sound (has a small subwoofer, extra headrest speakers)
-Adaptive LED headlights (vs fixed LED)
-Lane keep (which will stay disabled)


Additionally, the previous owner:
-Changed out the 195/50r16 tyres for 205/50r16 with a more aggressive compound.
-Deleted the sound tube
-Installed lowering springs, -20mm (0.75") height and +20% spring rate

First thing will be to get a baseline fuel economy. After that, I plan to raise the tyre pressure, install a lithium battery (from the Insight), underbody paneling, maybe a partial grille block, rear antenna delete (or smaller antenna). When it needs tyres it will get LRR rubber. Trailer hitch is probably in the cards. I also plan to get a tune (increases horsepower from 129 to 158) and see if that hurts or helps.

Some items that are interesting but aren't cost effective, that I'm window shopping:
Lightweight brake kit - 22.2lbs savings
Lightweight wheels - 15lbs savings
Lightweight seat rails - 13lbs savings

Along with the lithium battery (-19.5lbs), this would be a total weight savings of 69.7lbs, bringing the car down to (potentially) 2154lbs. There's another 10lbs to be shaved if I eventually go with aftermarket suspension.

[Ecky]

EDIT: Updated post.

First order of business was to get the infotainment (man I hate that word) into English, by having it flashed, since so many of the car's features rely on my being able to navigate it.







The cluster is still in Japanese, but it's easy enough to figure out what it's telling me.

After that, I filled up with 91 equivalent, and drove around Auckland. Middle of winter and it was sunny and 17c (62f).

[Ecky]

Edit: Updated post. All further items except mpg will be in metric.

After spending the night and accepting a job offer, I drove down to Wellington, where I'll be staying until further notice.

With an extra 120kg of junk in the car, driving exclusively with the top down at ~100-110kph, and climbing to 900m over ~400km, and some passing that required downshifts from 6th to 3rd, I averaged 37.6mpg or 6.3L/100km. That's a hair shy of the estimated average fuel economy.

On thing that surprised me is just how rugged New Zealand is. All of the roads are either winding or treacherously winding, with low speed limits that are still white-knuckle at times.

After getting over the mountains, I filled up again and drove at a more modest 90-100kph for the remaining 180km to Wellington. I was able to avoid passing and downshifting very much, and even with the top down I managed 49.4mpg or 4.75L/100km, beating the highway fuel economy estimate.









Here it is, parked at my bnb. I plan to add a pic of the city once I take one I like.

[freebeard]

Fastback aerocap?

[Ecky]

Originally Posted by freebeard

Fastback aerocap?

There's a targa version, but I'm going to be in New Zealand, and the weather ought to be beautiful almost year-round. Chances are good the top will only be up while it's raining. It's a necessary Cd hit.

[ECO-AKJ]

Originally Posted by Ecky

There's a targa version, but I'm going to be in New Zealand, and the weather ought to be beautiful almost year-round. Chances are good the top will only be up while it's raining. It's a necessary Cd hit.

One of my buddies have a mid 90's usa spec miata, he has a snap on cover that covers everything but the drivers seat and console, maybe something to look into for more top down fun!!

[freebeard]

Three-quarter tonneau or zippered?

TT-100 describes six different styles of tonneau cover which you may find on an MGA, only two of them being original factory issue.

[Ecky]

Originally Posted by freebeard

Three-quarter tonneau or zippered?

TT-100 describes six different styles of tonneau cover which you may find on an MGA, only two of them being original factory issue.

Now THAT is an idea.

[Ecky]

To me, a 48mpg highway fuel economy rating is outstanding. One of the pieces of that is Mazda's transmission. Here are a few fun bits about it:

Mazda managed to shave a full 46lbs out of the transmission, compared with the previous generation.

Gear ratios:
1st: 5.087
2nd: 2.991
3rd: 2.035
4th: 1.594
5th: 1.286
6th: 1.0
Final/rear: 2.866

With a tire diameter of 23.7 inches, that works out to 2400rpm @ 60mph. Compared with the previous (3rd) generation, that's 20% taller gearing with 33% lower engine displacement. Compared with the first generation of MX-5 (and we have a member on here who has had 50+ mpg out of one), the gearing is a full 30% taller, with 6% lower displacement. Pretty economical for a sporty car!

6th gear is also a 1:1 ratio, straight through without the countershaft. To keep highway RPM down, it has a very tall 2.866 rear differential. The previous generation had 4th gear as the 1:1.




The earliest versions of the transmission are known to be fragile, unfortunately. Cars with the larger 2.0L engine, stickier tires and limited slip differential have had failures in the first 30,000 miles. That said, I don't expect it to be a problem here.

[cRiPpLe_rOoStEr]

That's an interesting car. Though I'm not sure if you would be willing to try it, had it been me picking something with this engine, I'd be quite tempted to try running it on heavy fuels, like some sort of updated Hesselman engine.