Richard,

Thanks for running this test --- good data.  Although we suspected by
intuition, and reasoning, that 4th gear would have a lower MPG, but now we
know for sure.

A few observations:
- Taking the average of the averages, I get 14.6 MPG in 3rd and 16.85 MPG
in 4th.  This suggests over a 2 MPG advantage by upshifting to 4th gear.
-  But we do have look more closely at the data.  The difference at 50 mph
(average) is 1.45 MPG, the difference at 65 MPH is 3.05 MPG.  However The
one result that sticks out is 3.9 MPG difference in the "out" runs at 65
mph.  So this number is a question especially since "out" is slightly
downhill.  The anomaly in the data is in TPS.  For each test the TPS is a
lower number in 3rd gear, but in this instance (out at 65 mph) the TPS is a
higher number in 3rd gear (19.7 vs 14.5) which should cause us to wonder
why this could be the case.
- Actually drag increases as the "square" of velocity.
- The data at 50 MPH is more interesting, since I would always upshift well
before reaching 5000 RPM in 3rd.

And it made we wonder what question we (or I was originally) considering.
So looking at the data, I think the tradeoff is comparing "MPG" to "wear on
the engine".
- the cost of the higher gear is more lugging of the engine, and therefore
more wear and tear.
- the cost of the lower gear is more fuel.

Anyway, great data, thanks for running the test and reporting back!

Roland

On Mon, Apr 16, 2012 at 8:33 PM, Richard A Jones <Jones@colorado.edu> wrote:

> I followed this thread and decided to run some tests with
> my Syncro Westy with a Scan Gauge.  My idea was to run
> a piece of highway in third gear and in fourth gear and
> compare numbers.  I also ran a test at various speeds in
> 4th gear to see how speed changed things.
>
> I picked TPS, LOD, MAP and MPG for the Scan Gauge to
> report.  The first three, throttle position, engine load,
> and manifold pressure are reported from the ECU.  The
> last, MPG, is computed by some (unknown) algorithm by
> the Scan Gauge.
>
> I could do this because I have a Subaru 2.5 (OBD II).  I
> also have, for reference, stock gearing and 215/75-15 tires
> (27.8" diameter) and a heavy Westy.
>
> First the speed test.  Resistance goes up by the cube of
> the speed, or something like that.  Nothing here contradicts that:
> -----------------------------------------------------------------
> Varying speed test in Nevada (S of Boulder City) on April 8, 2012
>
>        S       G       RPM     TPS     LOD     MAP     MPG
>        75      4       3800    33      53      11.3    13.0
>        70      4       3600    23      43      10.7    14.7
>        65      4       3400    21      37      9.8     16.0
>        60      4       3100    16      31      9.8     16.3
>
> ------------------------------------------------------------------
>
> Now the comparison of speed and gear.  Two runs, two directions,
> 50 mph in 3rd and 4th gear and 65 mph in 3rd and 4th gear.
> Three or four readings were recorded and these are the averages:
> -------------------------------------------------------------------
>        S       G       RPM     TPS     LOD     MAP     MPG
> out     50      3       3900    8.7     21.7    4.6     20.5
> out2    50      4       2800    9       18.7    6.5     21.7
> -----------------------------------------------------------------
> back    50      3       3900    14      31.3    6.5     13.9
> back2   50      4       2800    16.3    28.3    9.1     15.6
> -----------------------------------------------------------------
> out     65      3       5000    19.7    39.7    6.3     13.8
> out2    65      4       3150    14.5    32.5    8.2     17.7
> -----------------------------------------------------------------
> back    65      3       5000    27      57      8.5     10.2
> back2   65      4       3150    45.5    52.7    10.9    12.4
> -----------------------------------------------------------------
> Out was slightly downhill and back was slightly uphill.   With
> one exception, it takes more throttle to go a speed in 4th
> than 3rd, but the load on the engine is less.  Mileage is
> better in 4th than in 3rd.
>
> Again, these are averages from one test run.  The raw data
> is at: http://jones.colorado.edu/VW/ScanGaugeTest.txt
> I wouldn't start a chip tuning company on these--I'd run at
> least one more test--or maybe a dozen.  ;-)
>
> Richard
>