re: MPG and Octane meets Myers Briggs

[jkerouac@xxxxxxxxxxxxx]

re: MPG and Octane meets Myers Briggs

This thread is now reminding me of a question on the Myers Briggs test.
It goes like: "Do you prefer practical application or theoretical
solution?"

I posted recently about my MGP and dyno testing, specifically describing
my engine tuning, and not a response to it.
If 30.6 mpg on a controlled run, 29 highway regularly, 22mpg on street
racing night, in a 3.2 liter //M3 on California's finest 92 octane is
not a statement, what is?
     If I try lower octane, the mpg is always down.  that has held true
for 20+ BMWs over 20+ years.  Comparing apples and apples, they all run
better MPG with higher octane.  One run in an old 2 liter 2000 with a
38/38 Weber DPS carburetor and 200+psi compression in all
cylinders(achieved with E12 9.5 pistons and a 121 head) with Sunoco 100
octane race gas was driving from New Jersey to Lime Rock, a day at the
track, and home again.  That got me over 20 mpg.
     We're not talking about power here, we're discussing effiency.  Two
different topics.
For many factors, from the higher specific power output of BMWs than
most other engines, to adaptive electronics that push the limits of
spark advance, to surface turbulance and flame front and mixture flow
technologies that allow compression ratios that will run on 89 octane
that back in the sixties needed as high a Premium as you could get.
     Formulation has an effect too.  I get the same power from 76 and
Chevron 92 but get worse mpg from 76 containing Ethanol than with
Chevron containing MTBE.
     And if the Shrub, as in little Bush, with his oil company buddies
in Washington would get off California's back there would be no MTBE
either.

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     In fact if you compete in a class requiring pump gas, here's a
trick to 'dope' the motronics for higher spark advance.  If you run over
100 miles hard on the gas with race gas, the ECU adapts to the higher
octane thus giving more spark advance at full throttle.
     When you switch back to pump gas, you get at least ten miles of the
higher advance that the ECU adapted to for the higher octane.  Typically
50 to 100.  I've measured an acceleration difference of about 0.1
seconds 60 to 80 in third gear.  That's certainly enough for a quarter
second of time per run at an autocross event.
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     As I hope it is shown, there are countless technological and
empirical factors involved here.  We could not begin to analyze the
principal component effect of each one.

     What I'm getting at is, just try it.
Go 1000 miles on name brand low octane pump gas.  Then go 1000 miles on
Chevron or Sunoco's finest.
Happy Driving,
'jk

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