Mike Marlow wrote:
> "Jeff" <kidsdoc2000@[EMAIL PROTECTED]
> wrote in message
> news:2bttj.126$kI4.4@[EMAIL PROTECTED]
>
>> The plural of anecdote is not data.
>>
>> We don't how he would have done if would have had even worse gas
mileage
>> if he replaced his V6 with a V6.
>>
>
> While your point is valid about anecdoti Jeff, it remains that
efficiency is
> a function of load and capability. An engine with more torque is going
to
> work less under the same cir***stances than one with less.
Actually, they will work the same, because they are putting the same
amount of power.
> I recently drove two identical model cars, but one was a 4 cylinder and
one
> was a 6 cylinder. Real world mileage experiences of people who own the
4
> cylinder versions are no better than those who own the 6's. I could
easily
> see why when I had a chance to really compare performallance. On a
stretch of
> interstate the 4 cylinder had to rev about 500 RMP higher than the 6, to
go
> at the same speed. That 4 was other wise quite impressive in terms of
its
> acceleration, etc. Geared differently to accommodate a poorer torque
curve
> than the 6, and less horsepower, made it at the very best, no better
than
> the 6.
Depends on how it is geared and driven.
But we're not quite on the same page. If you have a car that is not
underpowered, it is going to take the same amount of energy to move it
from point A to B. However, if if has significantly more power than it
needs, more than 150 HP for small car like a Honda Civic, then the
mileage will suffer.
> What people here have been saying is that there is real world
.experience out
> there on the street that defies the notion that all things being equal a
4
> will always be more efficient than a 6. It's simply not true. There's
not
> even reason to believe that it should be true.
Of course, it's not always true. There is no such thing as always.
It takes more energy to turn a bigger engine that a small engine.
Which takes more energy? To turn over big block Ford or the one-cylinder
engine on Dad's old lawn tractor? The big block Ford, of course.
There's more bearing surfaces to have friction, more air/fuel mixture to
compress, a large volume to suck air into.
While it is obvious for a huge engine compared to a small engine, the
same principle holds form a 2.0 Litre 4 cyl engine vs. a 2.5 litre six
cylinder using the same technology.
However, that doesn't mean that the difference is always going to be
huge. The Honda Accord 4 cyl (2.4 litre) only gets about about 2 mpg
more mileage than the 6 cyl (3.5 litre). So while the smaller engine is
more efficient, it is not hugely more efficient.
There are things you can do to make a engine have higher power output,
more all of which get more air or air/fuel mixture into the engine,
like more valves per cylinder, which allows more mixture or air to enter
the cylinder, add a turbocharger or super charger, which also pushes
more air into the cylinder or run the engine at a higher speed, which
does the same thing.
And there are things which increase the efficiency, like storing some of
the mechanical output of the engine as chemical energy (or electrical
energy) which can quickly be converted to mechanical energy via a motor
(hybrid), use Atkinson-cycle engine (like the Toyota Prius), use a
transmission which is geared well (my car has plenty of power to
maintain 70 mph at 2000 RPM, yet the car is geared to run at 3000 RPM,
so the engine seems more responsive), particularly one with an infinite
number of steps between the highest and lowest ratio (continuously
variable transmission, also like the Toyota Prius) and using variable
valve timing.
And, of course, how much mileage one gets is determined by how one drives.
Jeff
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