"Project 50 MPG Miata"
This webpage will be in a constant state of ""under construction"" for a while until I figure out what I am going to do.
Please drop by often to see where my progress is. Also, please cut me a little slack for the sloppy page. I promise I will
eventually get it straight.
Since April '03 (geez, has it really been that long) I have been working on a project to build a powerful and
lightweight Miata on a shoestring budget. After 5 Years and 1 Month I am calling it quits. I've grown tired of the
project and I'm looking for something else. I'd been thinking of building a high MPG (100 MPG) Geo Metro based car for
some time but I've switched gears and decided that a Miata based project would be a better choice. No, it won't get half
the MPGs that a Geo would but since we are Miata people and have Miata friends it should be the platform I use. This web
page will serve as a record of my attempt.
I haven't figured out a good way to incorporate some spreadsheets in this page so for now I am going to just provide a link to
a seperate page. On this page you
will find my MPG and any modifications done to the car as well as any future modifications I am planning. The MPG testing
occurs on the drive to/from work. This is a 16.3 mile relatively flat course (one way) with very few stop signs and only
light traffic. It takes me about 2 weeks to put 230 miles on the car so the testing process will take quite a while. From
time to time I will run ""real"" HWY MPG tests where I take the car out on the interstate for some pulse and glide driving
over a 100 mile course. I have never done this so the technique may take me a while to learn. Still, it will be very
interesting to see what they car can do on one of these long trips.
Yes, I am well aware that I stopped working on a really powerful and extremely great handling car, parked it, and started
building something very boring. Yes, I am also aware that in dollars the gas savings on such a car are not much. It is just
a project to keep me busy. You can stop sending me hate mail. If you want to build a 1000 HP Miata then please do so. This
is MY project .
In this project I will be modifying a gas guzzling (20 MPG average) '91 with a JRSC and a Link ECU. Here is the car getting
about 10 MPG! :
The first aerodynamic mod will be to close up the mouth of the car. Here is what it looks like before starting:
I took a Borla Exhaust banner I had laying around and used it for a temporary cover:
A 6" hole was cut in the center to allow just a bit of air to come through. In my testing I found that on a 93 degree day
I started overheating (water temp was up to 108C) if I ran the car at 5,000 RPM in 3rd gear for more than a mile or so.
Dropping back into 5th and slowing the engine down brought temps back to a normal 94C. I figure that I can easily stay in
normal operating temp during my average trip to work with this cover:
Below are just a bunch of notes and junk that are here for my future reference. Please ignore everything below this
Cost savings for a high MPG car:
180 work days x 33 mile round trip = 5940 miles
5940 miles / 20 MPG = 297 gal gas
297 gal gas x $4.00 for 92 octane = $1188 spent on gas driving to work
180 work days x 33 mile round trip = 5940 miles
5940 miles / 35 MPG = 170 gal gas
170 gal gas x $3.80 for 87 octane = $646 spent on gas driving to work
This gives me an expected savings on fuel of $542. I am not sure it is worth $542 a year to not be able to stomp the hell
out of the fun pedal and have the supercharger kick in but the project will definitely keep me busy for a while.
Some notes I pulled off a website for future use:
"http://www.cleanmpg.com/forums/index.php Tire pressures are a very important key to higher fuel economy. The higher the
pressure, the lower the rolling resistance, the higher the fuel economy. The absolute minimum you should use is the driver’s
side door or owners manual recommended tire inflation criteria. This is what the EPA and your car manufacturer sets tire
pressures to during the EPA city/highway testing. MAX sidewall is what I would recommend for most as it is well within the
safety limits of your car and tire and allows better FE than the pressure listed in the driver’s side door. I can discuss
but cannot personally recommend upwards of 25% higher than MAX sidewall as there are legal constraints we all have to live
with. That being said, 50 + #’s leads to even higher FE. Pros, higher FE, lower tread wear, more even treadwear across the
treads width, shorter braking distances in a variety of conditions, and in many cases, even better handling. Cons, higher
NVH (Noise, Vibration, Harshness)."
"Oil types and amounts are another important key to higher FE . A proper amount of low kinematic viscosity oil can do
wonders for not only longevity of your ICE but the FE your automobile may be capable of. You should use oil with a
viscosity that is within the band of your automobiles lubrication requirements. That being said, not all oils are the same.
If your automobile allows a 5W-20, you should be OK using a high quality Synthetic 0W-20. Mobil1 0W-20 has the lowest
kinematic viscosity as well as superior wear and breakdown properties vs. ANY non-synthetic I know of. About that level …
I recommend that instead of filling the case up to the high level mark that you instead use just enough oil to bring the
level up to between the high and low marks. You lose capacity in case of a leak and have a very slight increase in oil
temps but gain a slight amount of FE with a slightly lowered strain on the ICE’s frictional components."
blah blah blah:
"I get just under 12km/l (~27mpg) around town with a Link, 205/50x16 tyres (equiv to a 3.9:1 diff) at 34-38psi and tuned
for 15.5-16:1 in row1. Accel fuel has been lowered under 2k rpm, which can make it a bit lurchy...."
"Could prob do better, but I'd need to prob put something like 185/70x14 tyres on and stay out of boost too. It's kinda
hard when 20% TPS = 0 in vacuum ! So its not easy... being green ;)"
"For the aero and mechanical losses, I'd try the following:"
- 155/80/13 tires pumped up to max pressure. (need 1.6 brakes to do this).
- remove door mirrors and install a big wink mirror on the windshield header.
- cut holes in rear bumper cover.
- belly pan.
- hard top.
- lowered with front spoiler.
"- cover ""mouth"" in front bumper and duct air to radiator from under spoiler."
- 0w20 synthetic oil and MTL.
- smooth hub caps and fairings on rear wheel openings.
- Make sure brake slider pins are well lubed and all springs are in place.
For the engine - I don't know that just killing fuel to a cylinder is going to do much. You'll have a wider
throttle opening to help reduce the vac against the throttle plate... but that's about it. The rest of your frictional
and pumping losses are still there. I'd consider this stuff first:
- hot air induction.
- functioning EGR.
- Tune to 15.5:1 or leaner AFR under cruise.
- hottest thermostat you can find.
- loose PS and AC if you haven't already.
"There are a lot of engine/ECU tuning things you could try. If you have an Innovate LC-1, you could set 1 output
at 14.7=lambda, and the other output much leaner (just rich of misfire), and the rig a switch on the dash so you could turn
on ""lean burn"" mode (assuming proper Link tuning to go with this). This would probably be more efficient than killing 1
or 2 cylinders and having those run at stoich."
I suggest considering:
low resistance tires (or at least blow 'um up tight)
light weight wheels (obviously)
water injection (for knock resistance)
"several sizes of water jets, or preferably a variable speed motor"
low octane fuel (obviously)
195* thermostat (want as complete a burn as possible)
"extra slippery lubricants in engine, tranny, & diff. (Obvious Man at work again)"
free-flow exhaust (maybe)
scavenging header (maybe)
hot range spark plugs
wide band sensor (obviously)
EGT gauge would be nice as well
tune your Link so the cruising zones are considerably enleaned (experimentation required)
"Log your knock sensor and simply enlean ARF's slowly till knock, then add a bit more water. Repeat."
"When additional water will not quell the knock, back up to the previous settings. I think you could run on all 4"
cyls and still get some decent mileage.
"I've run 16-17:1 in the Mazda, it feels anaemic and tinny. Around town it gets really jerky too, so it's prob a
motorway only deal ..."