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From: Jesse on 5 Jul 2010 23:42
I had a discussion with a pal about comparing vehicle fuel economy.
Would a 6 Cylinder at 65 MPH showing 2200 RPM use less fuel than a 4
cylinder showing 2600 RPM at 65 MPH?
From: Tegger on 6 Jul 2010 08:14
Jesse <sumin(a)telus.net> wrote in news:ib95361v126e4f9msaaovpehaaa7o2i9eh@
4ax.com:

> I had a discussion with a pal about comparing vehicle fuel economy.
> Would a 6 Cylinder at 65 MPH showing 2200 RPM use less fuel than a 4
> cylinder showing 2600 RPM at 65 MPH?
>


I think the question is impossible to answer as a generic thing; there are
too many variables.

What are the characteristics of each engine and each car? How much power is
being created by each engine, and where in their rev-range? How heavy is
each car? How much wind-resistance has each car? How much throttle-opening
is required to maintain speed in each car?

--
Tegger
From: Don Stauffer on 6 Jul 2010 09:37
Jesse wrote:
> I had a discussion with a pal about comparing vehicle fuel economy.
> Would a 6 Cylinder at 65 MPH showing 2200 RPM use less fuel than a 4
> cylinder showing 2600 RPM at 65 MPH?

It's not the number of cylinders, it is total displacement. A big four,
say a 3 liter four, is likely to get poorer gas milage than a 2.5 liter
six, all else being equal.

That all else being equal is a big gotcha, though. One of the most
important parameters is final drive ratio (used to be rear axle ratio in
days of rear drive cars).

After the first gas embargo in late seventies, Ford offered a high
milage version of the Mustang, the Mustang MPG. Only difference was
final drive ratio.

While cylinder sizes are narrowing, in olden days you could find very
big cylinders on some cars, very small ones on others.
From: jim beam on 6 Jul 2010 10:24
On 07/05/2010 08:42 PM, Jesse wrote:
> I had a discussion with a pal about comparing vehicle fuel economy.
> Would a 6 Cylinder at 65 MPH showing 2200 RPM use less fuel than a 4
> cylinder showing 2600 RPM at 65 MPH?

all other factors being equal, the 4 will be more efficient because of
the lower component count and therefore lower friction losses. BUT,
it's not that simple in real life, and all factors are not equal - a
well tuned 6 can easily be more efficient than a poorly tuned 4. so,
there's not "definitive" answer to your question unless you want to
compare specific vehicles/engines.


--
nomina rutrum rutrum
From: ben91932 on 6 Jul 2010 10:30
On Jul 5, 8:42 pm, Jesse <su...(a)telus.net> wrote:
> I had a discussion with a pal about comparing vehicle fuel economy.
> Would a 6 Cylinder at 65 MPH showing 2200 RPM use less fuel than a 4
> cylinder showing 2600 RPM at 65 MPH?

All other factors being equal, a 6 might show a few % less effeciency
than a 4 due to friction. (more surface area of piston/ring and more
rockers/cam followers)
Does this sound reasonable Dan S.?
Ben
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