Re: Why you should never buy a car without a tachometer

"Dave" <nofreeknway@xxxxxxxx> wrote:
>> Anyway, when you get a modern car, even one as modern as
>> Dave C's, don't expect it to get best mpg above 60 mph (or
>> at 40% of redline, for that matter).
>>
>> Expect best mpg at the lowest speed at which the powertrain
>> will run in top gear with no powertrain slippage (locked TC
>> clutch, or manual trans).
>>
>> BTW: I don't see anyone recommending that people actually
>> drive at best-mpg speed. My time is worth too much to me,
>> so I drive faster whenever safely possible.
>> --
>> Chuck Tomlinson
>>
>
>Now see Garth, I knew someone was going to try to come up with an excuse, or
>call you a liar. After all, it is a mortal sin to drive faster than 50MPH.

Are you trying to *invent* an agenda? Who suggested that
you (or anyone else) shouldn't drive faster than 50 mph? I
cruise at 75-80+ mph frequently, even though I have data to
show that my car is more economical at lower speeds.

>:) We just CAN'T have people believing the truth that many cars get better
>fuel economy at faster speeds. THAT JUST WON'T DO!!! :) Forget the fact
>that Otto Cycle engines haven't significantly changed in about a century.
>Your car is so old, it doesn't count. (!)

Actually Dave, the *age* of Garth's car is not the issue.
The *design* of his car is the issue.

I doubt that his car delivers optimum mpg at ~65 mph in
proper tune but in its current state, the likelihood of poor
fuel mixtures and an energy-wasting transmission design may
mean that his car peaks at a higher speed than a modern car
with constant mixtures and energy-efficient transmissions.

If his engine is in poor enough tune, and his trans is
"sloppy" enough, he *could* have an mpg peak near 65 mph.

But I *know* that *your* car does not deliver best economy
anywhere near 78 mph. It *cannot* sustain 42 mpg at 78 mph
on level ground in still air.

I don't think you're a liar, because you seem to believe
what you're saying. You're simply *wrong*, but you don't
know enough to realize it, and you'd rather wallow in
ignorance than allow yourself to learn.

>Yesterday, I found another source, an engineer working on engines used in
>4X4 off-road vehicles. Yes, they are Otto Cycle engines. He stated that
>maximum fuel economy will be achieved around 60% of the engine's RPM at
>(maximum horsepower RPM).

At what load? At what vehicle speed? If you don't know why
engine load and vehicle speed matter, read (and understand)
Todd Wasson's long post, or continue to embrace ignorance
and make a fool of yourself.

At 60% of peak power rpm in top gear, my car is running at
~125 mph, and 65%-70% of full-throttle torque (probably just
short of power enrichment). IOW, my engine is operating
very close to *maximum fuel efficiency* at 125 mph.

My car is EPA-rated at 18 city/24 mpg highway. If the
engine is most fuel-efficient at 125 mph, as I (and your
source du jour) think it is, what fuel economy (mpg) should
I expect at 125 mph, Dave? Anyone?

BTW, why have you not tried to answer any of the questions
I've asked you in this thread?

>[...] ***, the
>experts who are telling me how to figure the RPM of maximum fuel efficiency
>can't ALL be wrong.

1. No expert believes that maximum vehicle fuel economy
necessarily (or even occasionally, in modern cars) occurs at
the engine's most efficient operating state (rpm and load).

2. There is no such thing as "the RPM of maximum fuel
efficiency". Maximum engine fuel efficiency occurs at a
combination of rpm *and load*.

3. The engine's most efficient load/rpm point is irrelevant
to the vehicle's most economical cruising speed.

>Maybe I should donate my car to science, as it's
>obviously got some kind of alien technology in it's Otto Cycle engine, or
>else it wouldn't ACT like an Otto Cycle engine. (!)
>
>Welcome to the liar's club, Garth. Stop posting the truth that your engine
>is most fuel-efficient at 64MPH. Either that, or be prepared to be called a
>liar. -Dave

Keep your car. Learn from people who know a lot more than
you do, Dave. Either that, or prepare to (continue to)
prove yourself a fool.
--
Chuck Tomlinson


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