Miata Mailing List: December 1993, Message #199
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   From: suskind@isdev1.melpar.esys.com (Barry A. Suskind)
Subject: Re: Texaco - Ethanol vs. MBTE - (Mileage)
   Date: Wed, 22 Dec 1993 07:55:50 -0500

[Herb Samuels ] Writes:
> 
> I have a 1990 and have always gotten at least 27-28 mpg driving in the
> warmer weather at varying speeds and up to 80 mph with shifting at
> more than 4,000 rpm.  In the winter with MBTE last year I got about 1
> mpg less.  This summer I had a BBR turbo installed and have noticed no
> change in the mpg I get even though the car has about 50% more torque
> and horsepower.  This is probably because there is much more torque at
> 2,000 to 3,000 RPM so its not always necessary to rev the engine at
> very high RPMs.  In any case 22 mpg seems somewhat low to me unless
> you are doing many very short trips which does not allow the engine to
> opperate at its most effieient temperature.  Also 22 mpg at 70 or 80
> mph seems also low since I used to get at least 27 mpg at those speeds
> even when my car was stock.  Could Mazda have tuned the engine
> differently after 1990 or can anyone think of other reasons for the
> wide difference in mpg we measure.
> 
> Herb Samuels
> 
> 
> 
> 

For one driving habits will DRASTICALLY change gas milage. Do you normally
stomp on the gas pedal or do you ease into it? Do you always upshift to the
next higher gear or keep the car in the low gears regardless of weather or
not you are increasing your speed? Do you redline every shift?
If you make lots of short trips, of less than 5 minutes, the car never warms
up and your gas milage will stink as the car never gets to its operating range
and when the car is cold the fuel to air mixture is richer to keep the car
running (choke). The outside weather has LOTS to do with it. If you live in
high altitude climates your gas milage will be worse due to the lower air
pressure. If you live in the desert the hot air will also make your car perform
worse. If you live in cold climates it will take much longer to heat up the
car to operating temperatures and your gas milage will also suffer. Your gas
milage will also suffer with the top down, running the AC (with or without the
top down). I tend to get the best gas milage in the spring and the fall when
the tempuratures are around 50-60 degrees. When the temperature is cooler 
the cooler, denser air will aide performance. However, not such that it takes
too long to heat up the car like in winter (this is why in cars with turbos do
better with intercoolers). Also in the fall you are less likely to have the top
down because it is a little too cold.

Also since every engine is not blue printed there are lots of variances in
the tolerances in the engine. This may give you slightly higer compression,
slightly different cam profile, etc. This may change performance a bit.

I do mostly highway driving to and from work, about 50 miles per day running
around 70 mph. I usually get close to 30 mpg in the spring and fall and closer
to 25 mpg in the winter and summer. I have also found that gas milage has 
improved with age. When the car was only a year old I only got around 25 mpg.


-----  Barry A. Suskind, Information Services, E-Systems Melpar Division -----
----------------  7700 Arlington Blvd, Falls Church, VA 22046 ----------------
----  Internet: suskind@melpar.esys.com ----------- Ma Bell: 703-560-5000 ----
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