Date:         Wed, 20 Apr 94 21:15:44 CDT
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Joel Walker <JWALKER@ua1vm.ua.edu>
Subject:      Re: thread on underpowered?

>For comparison, the last time I checked fuel usage around town I got around
>19 mpg, but then I tend to drive boxer VWs with the pedal to the floor just
>about all the time, a habit I developed with my old '58 bug.
>So what gives?  Why am I getting better fuel economy than Joel?  If the
>best Joel can get is 23 mpg, I ought to be getting 13.

well ... yours could be a tad lean and mine could be really screwed up rich.
or you could have that mythical 200mpg Bosch EFI. :)  i've always figured
mine was about right, cause the 80 bus got 18.6 average over 110,000 miles.
i got 25 mpg a couple of times in it, and could consistently get over 20mpg
on trips.

it is possible that my 'gentle' technique (rev up to 4000 and shift; shift
down whenever the rpm drops to 2000-2500, depending on load/hill/etc) is NOT
the best way to get good economy.

BUT ... with my handy dandy trip computer, i did some semi-serious testing
at steady (cruise control) rpms ... clocking the fuel consumption over ten
liters or so (takes about an hour at each rpm). and this is what i found:

4000 rpm  4.3 min/liter => 18.1 mpg   at 67.0 mph
3800 rpm  5.1 min/liter => 20.4 mpg   at 63.7 mph
3600 rpm  5.5 min/liter => 21.0 mpg   at 60.7 mph
3600 rpm  5.7 min/liter => 21.7 mpg   at 60.3 mph
3400 rpm  6.3 min/liter => 22.8 mpg   at 57.0 mph
3400 rpm  6.4 min/liter => 23.1 mpg   at 57.0 mph
3200 rpm  7.2 min/liter => 24.2 mpg   at 53.6 mph
3000 rpm  8.1 min/liter => 25.6 mpg   at 50.3 mph

(you try cruising at 50 mph on the interstate! talk about pissing people off!)

now .. when i did kinda the same thing (except not for a whole hour) in my
86 bus, it had a more 'humped' mpg curve ... best economy between 3200 and
3400, then 'acceptable' economy down to 3800, and really bad economy from
4200 rpm onward. the funny thing was that it pretty much leveled out at about
19 mpg from 3800 to 4200 rpm, which is 64 mph to 70 mph. i did try to drive
the same route each time, so the data would be for the same terrain.

now ... how correct and scientific is this? probably not much. no guarantees
on the calibration of my trip computer, brands of gasoline, terrain, road
surfac friction, altitude, etc., etc., etc.  i'm looking for 'pattern' data
... so when my bus changes its pattern, i'll notice it (i.e., something has
changed ... so something must be wrong!).  but since the values were pretty
much in the ballpark of my 1980 bus, i figured it was likely correct enough.
(since the overall shape and the weights are pretty much the same).

anybody else keep track of their mileage? anybody anywhere close to being as
anal-retentive? :)

joel