Read this gem about GM

#11

<uccoskun (AT) gmail (DOT) com> wrote

Quote:

A brain storming about fuel economy: Fuel econom is a complex equation
like many things in life.

1. bigger engine does not mean worse fuel efficiency (i.e same car with
two different engines have almost same mpg). however, bigger engines
comes in heavier cars, and this is the main reason why bigger engines
do worse on mpg side.

I agree that engine displacement does not necessarily relate directly to gas
mileage.
There are other factors involved here.

Quote:

2. the american engines (push rods) have worse efficiency than smaller
ones (timing belts)

Huh? You can have timing belts and still have pushrods...Or chains, or
gears.
Same goes for OHC engines. Pushrod engines can be relatively very
efficient.
Your point is what I would call a 'non sequitur' (sp?)

Quote:

3. the weight of the cars is the main reason in low mpg in city
driving, this is the main reason why american cars do worse in city
driving.
In stop start driving, the engine is not operating for long periods at the

most
efficient range. There are periods of idling, periods of gasguzzling
acceleration that
are not in effect at constant speed highway driving.

Quote:

4. aerodymanic determines the fuel economy on high way driving.
(Newtones law of inertia says, mass/weight is not important after you
increase your speed to a certain speed)

Aerodynamics make a difference as does the total component of rolling
friction.
(I mean the total contribution of tires, bearings, gears, transmissions,
engine....the whole
bloody tortilla)

Quote:

5. the manual cars are better than automatic cars. due to many gears to
rotate.
We used to believe this was universally true, but it is not necessarily so

any more.
Auto trannies can get you better mileage than manuals.

Quote:

6. 2 wheel drive cars are more efficient than 4 wheel drive cars
This has traditionally been true, but I think the gap has narrowed.

Probably still true due
to the almost certainty that the total component of friction is greater
than a similar 2 wheel drive.

Quote:

7. diesels are more efficient due to hight comprssion (temperature) in
the engine.
Diesels are still in development, but can deliver a lot of power with low

fuel consumption.
Just read an article about a diesel breaking the diesel land speed record
impressively. RPMs were
higher than you would think possible. A modern turbodiesel can give you
power and economy.

Quote:

8. keep your thermostat at OEM because 100 C and 70C engine
temperatrues means almost 10 percent efficiency change due
thermodynamic.
Unchallenged. You have to run the engine at the design temperature. Look

back at Smoky Yunicks attempts
to interest the auto industry in an adiabatic engine, running at very high
temperatures. It was very promising, but
needed a lot of development. Ol Smoky and the American car industry never
got together on it, IIRC:

#12

In article <1165164659.010345.269940 (AT) 73g2000cwn (DOT) googlegroups.com>,
uccoskun (AT) gmail (DOT) com wrote:

Quote:

A brain storming about fuel economy: Fuel econom is a complex equation
like many things in life.

1. bigger engine does not mean worse fuel efficiency (i.e same car with
two different engines have almost same mpg). however, bigger engines
comes in heavier cars, and this is the main reason why bigger engines
do worse on mpg side.
In city driving the larger engine does worse. In highway driving at

higher speeds the larger engine may do better.
I'm assuming all other factors are equal. Now days there are a number
of design changes coming on the market that make it hard to generalize
here. For example VVT makes engines better over a wider range of
operating conditions, also switching of cylinders may improve mileage.
The cylinder switch off is usually only at easy highway cruising.

Quote:

2. the american engines (push rods) have worse efficiency than smaller
ones (timing belts)
Not always true, multi valves in smaller engines may reduce economy at

certain speeds.
My base for this is my measured comparison of the Chrysler 2.7L V6
(multi valve overhead cam) and their 3.3L V6 (push rods) in similar cars.
I'll admit my research here is limited to only two engines, however I
have read reports of other multi valve engines that also show lower
mileage under certain conditions.
Overhead cam and multi valve engine designs mainly achieve higher
horsepower.

Quote:

3. the weight of the cars is the main reason in low mpg in city
driving, this is the main reason why american cars do worse in city
driving.
Yes, but as I said in 1. the larger engine is a big factor in this.

I assume you are talking about gasoline engines, where the efficiency is
lower at low power output and when idling a larger engine uses more fuel.
Diesels which always input the full amount of air run much more
efficiently at low power output.

Quote:

4. aerodymanic determines the fuel economy on high way driving.
(Newtones law of inertia says, mass/weight is not important after you
increase your speed to a certain speed)
Agreed, air resistance becomes a greater factor as speed increases.

However hilly roads will result in higher fuel consumption for the
heavier vehicle.

Quote:

5. the manual cars are better than automatic cars. due to many gears to
rotate.
Nope, modern automatics equal manual shift for fuel consumption in both

highway and city driving.
The CV transmissions improve automatics even further.

Quote:

6. 2 wheel drive cars are more efficient than 4 wheel drive cars
Of course, less drive line power loss. Only a few 1% with modern

vehicles.

Quote:

7. diesels are more efficient due to hight comprssion (temperature) in
the engine.
It's the high compression at all RPMs (not just the temperature) that

give diesels higher efficiency than the typical gasoline engine. The
diesel always inhales the full amount of air, so the cylinder pressure
is always the same before combustion. Gasoline engines do not inhale
the full amount of air at lower power levels, therefore they do not
achieve their compression capability.

I just read a report on the new E Class Mercedes 3.0L Bluetec diesel
which beats the equivalent Mercedes gasoline engine in all respects,
both for fuel efficiency and effective power. I'm wondering if it has
the diesel stink?
Sounds like a great engine, tons of torque which is what moves legally
driven vehicles along.
http://research.cars.com/go/crp/rese...ion=summary&af
f=national&call=crp&makeid=31&year=2007&modelid=28 7

Quote:

8. keep your thermostat at OEM because 100 C and 70C engine
temperatrues means almost 10 percent efficiency change due
thermodynamic.
Yes.

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Read this gem about GM

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Re: Read this gem about GM - 12-06-2006 , 11:03 AM

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