Re: If you want to be invisible on a car lot...

frkrygow@xxxxxxxxx wrote:
Bill Baka wrote:
Mark,
You must be one of those who really flunked physics, BADLY.
I did this with a 1961 Rambler flathead 6 and took it from 25 MPG up to
38 MPG+ on the highway at 65 MPH.

From _just_ a change in gear ratio? Sorry, but that sounds _very_
implausible.

If you have a car, and a stopwatch,
and can make a fairly reliable measurement, then try something before
you go all self righteous on me. I took my 4,400 pound 1966 Chrysler
with the 2.73 rear end and 440 engine, and timed the coast down from 70
to 60. It was 15 seconds in neutral, but only 7 seconds in gear with a
727 automatic. The SIMPLE deduction is that half the energy was wasted
just rotating the engine.

It's SIMPLE, all right, but it's wrong. At least, if you imagine it's
just piston ring friction at work.

Not friction, inertia. Lower RPM and more torque make better use of all those cubic inches.

The great bulk of the coast-down difference you described comes from
fighting the compression and the pumping losses of the engine, not just
the friction of the piston rings and other moving components.

No pumping losses when the throttle is closed, just piston losses.

Big DUH, bicycle genius.
Do the math and see how much energy it takes to make each 2 pound piston
accelerate and decelerate up and down at 2,500 RPM.

Sure, it takes energy to accelerate a piston. That energy comes almost
entirely from the nearby piston which is decelerating. They are simply
trading kinetic energy back and forth.

Not so.

Have you taken a thermo course? If so, imagine a control volume around
the engine. If your losses were just energy accelerating and
decelerating the piston, how would the energy leave the system?


You should be aware of variable displacement engine technology, in
which certain cylinder's valves are kept closed.

Those are a joke from a purist's point of view and I am a purist.

The result is more
gas mileage, largely because of less pumping loss.

Less pumping loss but not less displacement or piston inertia.

If auto makers
could get the same result by just raising gear ratios (and programming
for rapid downshift when necessary) they'd certainly take that less
complicated approach.

Only if they were forced to.

- Frank Krygowski

Have you noticed the emphasis on horsepower in spite of gas prices? The car makers are only making a big show out of better mileage cars. They are not serious yet. I or maybe even you could make a car that got 40 MPG minimum under any circumstances but yet hybrids and fuel cells get all the news. What about an ordinary car with small batteries and regenerative electric motors for stop light boosts and traffic jams. That does not need high tech or fuel cells or anything a good tinkerer could not do.
Damn, It is NOT rocket science.

Bill Baka
.

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