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Old 11-22-2009, 10:46 PM   #116 (permalink)
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Location: 1000 Islands, Ontario, Canada
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Blackfly - '98 Geo Metro
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Last 3: 70.09 mpg (US)

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Some speed vs. MPG results

majestic: thanks for that image. The eventual permanent/removable version won't look that nice!


Did some testing today. Several significant disclaimers follow...

The chart shows speed vs. MPG in bi-directional runs on the same stretch of road.

Green line was a "baseline" for the car (included partial grille block & rear skirts),

Yellow/orange after installing the transmission with the taller final drive,

Blue = boat tail

Disclaimers: Also, the fuel use offset I'm using on the ScanGauge now is higher than those 2 tests (I don't think I recorded it then, actually), so all else being equal, my displayed MPG is actually slightly less now than it would have been then.
  • The 3 tests aren't strictly comparable for a bunch of reasons, not the least of which is weather conditions (temp) differing a lot
  • Ethanol in fuel now (5 or 10%, I forget which), but not when the first 2 tests were run
  • Cruise control was used for the previous testing, but I used my foot today. Even though I managed to keep the average speed dead on for 9/10 one-way runs (one run was off by 1 mph), the average doesn't tell the whole story - it's no where near as precise/consistent as cruise control.
  • The car is older, different weight oil in the engine, tires are more worn, spark plugs are probably worn more, etc. etc.

So take this as an "actual mileage may vary" comparison. The relative comparisons are not really accurate. But there's no doubt the absolute figures are satisfying, and they should get even better when I stick the undertray back on.

I'm going to try to do the A-B-A one day this week - its results should be a bit more accurate for relative numbers.
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Latest mods test: 15 mods = 15% MPG improvement: A-B test, 2007 Honda Civic 1.8L, 5-speed
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has launched a forum for the efficient new Mitsubishi Mirage - fuel efficiency info for Geo Metro owners - electric car conversion on a beer budget
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