[Miata] Fw: Replacing rear window

Thu Jul 3 09:26:08 CDT 2008

Previously on Replacing rear window, <mark.ariagno at boehringer-ingelheim.com>
said...

>  Its a compromise.  Keeps me with my wifes blessing from a motorcycle.
> She wants me around for a while.  But I think some after market things, I
> can squeak a few more mpg out of her.  Heck it is a 1.8 L engine and the car
> weighs nothing.  But you are right she loves 6k to 7K rpm.
>
> Fiat spider got 34 with a few mods plus improved performance.  So mazda
> magic can happen too.  Fiat was easier, no computer and sensors.
>
I'd argue that the Miata is easier.  Because of the electronic engine
controls there's almost nothing you can/should/will want to do to it.

A lot happened in the 20 years (give or take) between the 124/2000 Fiat and
the Miata, and it's important to not mix apples and oranges.

The Fiat that most people remember (and the best comparison to the Miata),
the 1980-82 fuel-injected Spider 2000i has a 2.0 liter engine which is
capable of producing 102 hp at the crank and got an average of 24 to 25 MPG.
That compares in output to the 1990-1993 1.6 liter Miata engine which is
rated at 116 crankshaft horsepower.  That car, my car, averages 28 MPG in
mixed driving and gets 32 on the highway.  Your 132hp 1.8 liter Miata is an
orange.  With more power (if you call on it) comes higher fuel consumption.
Both cars do weigh about the same, and with a final drive ratio of 3.9:1 for
the Fiat and 3.34:1 for the Miata I'm willing to call them apples, although
the Miata has the advantage.  That brings us back to the horsepower
difference, and that's where any difference in fuel economy comes in.  While
the Fiat may have been capable of a couple of extra miles per gallon, it's
because it had less power and so burned less fuel.  My quick research
indicates that in mixed driving the Fiat gets 23-26 MPG.  That's two to five
MPG *worse* than my 1.6 liter Miata which produces 14 more horsepower, and
its within a MPG or two of your '97 Miata's average fuel burn while it's
capable of making 36 horsepower more and meeting EPA requirements that the
Fiat never saw.  I'm not trying to be defensive here, I just want to keep
things in perspective because very simply there is almost nothing you can do
to improve the fuel economy of the Miata other than lifting your right foot.

The reason the "magic" you mention worked on the Fiat is because it had room
for improvement.  No fault to Fiat, just that 20 to 30 years ago the
technology wasn't there to get as much out of the engine (one of the reasons
you can get 138 normally aspirated hp from a 1.8 liter engine now when Fiat
got 94 from the same displacement in the Spider 1800.  Electronic engine
controls combined with EPA and ARB regulations mean that most of the magic
has been performed at the factory already.  In the case of the Miata, it is
optimized well enough from the factory that when we talk about performance
enhancing mods, nobody uses a chip.  The ECU is dialed in that well.

That said, one of the best performance improvements you *can* make on a NA
car (1st generation, not Normally Aspirated), is to move the base timing up
a few degrees.  By advancing the timing from the factory setting of 12° BTDC
to 14°, 16°, or even 18°, you will improve the car's pull at lower RPM and
at the same time marginally improve your fuel economy.  This comes at the
expense of knock margin which is reduced as you advance the timing, so it's
important to keep an ear out for knock/ping and get off the throttle if you
hear it, then either adjust your timing or octane accordingly.  I'm going to
assume that since we want best economy you will want to stick with 87 Octane
(US) gasoline.  That assumed, I'd start at 16° BTDC and see how the car
likes it.  If it pings when hot or under hard acceleration, back it down to
14° and try again.  Leave it set at whatever timing allows it to run without
pinging.  The procedure for adjusting the timing is incredibly simple and
completely free.  You can read about it here:
http://www.miata.net/garage/ignition.html#timing

As to your overall quest is for a fun but economical car, I think you've
come as close as you're likely to.  The 1.8 Liter NA Miatæ average in the
mid to upper 20s for MPG.  I would think that most will get 30 on the
highway with the top up and speed at 65 or lower (with the tall gearing
faster is thirstier).  It's no motorcycle, but for the performance it does
pretty well.  Any improvements in physical performance will come with a fuel
penalty and while your right foot has direct control of fuel economy, it
comes at the expense of the fun factor, so you strike your own balance.

As Larry said, the 6-speed will not help you in the fuel economy department
at all, and most who own one say they preferred their 5-speed, so my advice
is to save your money there.

The front license plate issue is annoying, but you're not the first to have
gone down that road.  There are write-ups online detailing various
solutions, the simplest being a plate that hangs inside the radiator opening
by hinges and swings back when the car starts moving to allow the radiator
to breathe.  There are mounting holes under there that were designed for the
OEM front plate bracket that can be used for the purpose.  Of course there
are others who just leave the front plate off and take their chances.

As to the timing belt, you can save yourself the effort of "looking" as you
can't accurately determine its condition by just looking at the belt.  By
the time you get in there enough to look at the belt you might as well
replace it, along with some seals and the water pump while you're at it, not
that those are common failure points but it's a PITA to take it all apart
again a few months after a timing belt change because the water pump (now
stressed by a tighter belt) has started to leak.

Finally, welcome!  I think that you'll find the Miata is all the fun of the
Fiat you remember, and none of the work to maintain (BW excepted).

    -John
------------------------------
John Freas <%20john7690 at comcast.net>
1992 *YELLOW* "Sting<http://john.freas.home.comcast.net/pix/sting/sting.html>
"
1995 Black R Package
"Spike<http://www.geocities.com/clash_girl/Spike_Scrapbook.html>
"
Elizabethtown, Indiana
- Standard Disclaimer
<http://john.freas.home.comcast.net/disclaimer.html>Applies -
Team LS1,2, SP, the Gap...
I love my Miata
girl<http://www.geocities.com/clash_girl/Spike_Scrapbook.html>and my
Miata Baby
"I have no idea what those dimple things on the windshield frame are for."
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