Re: Fuel economy (was Re: Pressure Acummulator Discoveries)

[John Greenstreet <jgreenst@motown.ge.com>]

> From quattro-owner@swiss.ans.net Tue Aug  2 18:52:52 1994
> From: Eliot Lim <eliot@u.washington.edu>
> X-Sender: eliot@homer06.u.washington.edu
> Subject: Re: Fuel economy (was Re: Pressure Acummulator Discoveries)
> To: quattro@swiss.ans.net
> Date: Tue, 2 Aug 1994 15:19:48 -0700 (PDT)
> X-Mailer: ELM [version 2.4 PL23]
> Content-Type> : > text> 
> Content-Length: 527
> Sender: quattro-owner@swiss.ans.net
> Reply-To: quattro@swiss.ans.net
> 
> >A manual 5
> > speed Audi has better fuel economy for two reasons - less transmission
> > losses and "deceleration fuel cutoff" (shuts off injectors when the car
> > is in gear, clutch not pressed and throttle closed). 
> 
> 1) deceleration fuel cutoff is not limited to manual transmission cars
> only.  my v8 has it and it's slush.
> 
> 2) a 5 speed will deliver better economy if and only if the driver is
> smart enough to take advantage of it.  a smart slush can produce better
> fuel mileage than a dumb driver with a 5 speed.  
> 

Eliot is right on the money here.  When my girlfriend went from a
5-speed 5-cyl Audi 80 to a 6-cyl, 4-speed auto 90, her mileage actually
increased despite the 90 being a larger, 400 lb heavier car.  Of
course, the newer engine management of the V6 and the V6 itself
deserves some of the credit, but she had a habit of always shifting too
late (as most people do) for a given acceleration rate, and therefore
her mileage was very poor with the stick.

I'd like to see a test of the new type auto used in the 100 from '93
on, i.e. one with Dynamic Shift Program (DSP) selection.  As this
transmission determines the shift program based on how actively the
driver actuates the gas pedal, it has no Sport/Economy switch.  All the
tests I've seen so far have been with the conventional automatic
used in 1992 100s.

I've driven the new DSP box many times and when it senses economical
driving habits, it shifts very early and will not downshift unless you
depress the throttle quickly.  In the most economical program, engine
revs will not exceed 2000 rpm until the car goes over 45 mph (where
revs are dependent on speed in top gear).  As the overall ratio in high
gear is slightly longer than that of the same car with a 5-speed,
economy should be comparable to that of a properly-driven 5-speed and
better than what most would achieve with the 5-speed.

Too bad they ditched the trip computer in '93, that would have made
comparisons easy!

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John Greenstreet, Senior Engineer           (jgreenst@motown.ge.com)
Martin Marietta Government Electronic Systems    Moorestown NJ 08057
WPI Class of '75, Temple Class of '94

My new car history:
1972     1975       1978      1982       1986        1989      1992
 VW  ->   VW    ->  Audi  ->  Audi  -> Mercedes -> Mercedes -> Audi
SBug   Scirocco   Fox GTI     4000S    190E 2.3    190E 2.6    100CS

POSSLQ's* new car history:
         1978       1981       1985      1988        1990      1993
       Triumph ->  Toyota ->  Toyota  ->  VW    ->   Audi   -> Audi
       Spitfire    Tercel     Corolla   Jetta GL      80       90S

*POSSLQ = Person of Opposite Sex Sharing Living Quarters
Note: All Audis and Mercedes above were sold to friends or family.
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