My 1974 Dasher had the upshift light. Karl Wolz Sent from my electronic umbilicus On Apr 18, 2012, at 5:06 PM, Kent Christensen <lkchris@OSOGRANDE.COM> wrote:
> Re: Given the anomalies with the reported 65 mph data ... > > > Some may recall in the 1980s that VW Golfs (and others) had an "upshift > light" on the dash. (Maybe it was the '70s in which case it was "Rabbit.") > A prod to do just that and useful for at least two reasons: > > 1. An engine running twice the rpms as another is very nearly equivalent to > a twice as large engine running the same speed as the smaller engine. Since > gasoline engines mostly run near stoichiometric fuel/air ratio, it's nearly > a direct relationship with fuel consumption increasing with engine speed, as > the wider throttle opening permits consumption of more fuel/air mixture. > > 2. AND ... any throttled engine consumes power just running itself by > virtue of the effort required to "suck" air past a partially closed > throttle. Called pumping loss. The upshift at low rpms usually results in > a wider open throttle condition, also increasing fuel economy. > > Lots of interesting contrasts here with a diesel engine as they change > speeds not by increasing air/fuel quantity but rather by simply burning more > fuel to the same amount of air---yes, diesels don't have throttles and > concurrently don't suffer pumping losses as a result. At whichever speed a > gasoline engine is running the fuel/air ratio is nearly always near 15 air/1 > fuel, while a diesel could run at idle at near 150 air to 1 fuel (helping > explain why an idling diesel cools down). > > And, indeed greater speed equals greater drag, but at the same speed the > gasoline engine running at lower rpm (higher gear) quite obviously burns > less fuel. > > Kent Christensen > Albuquerque > '81 Vanagon (owned since '83) > and '07 Merc GL320CDI and '08 BMW R1200RT, '02 BMW R1100S, '84 BMW R80G/S |
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