Engine type & Fuel Economy

First off, I know nothing about cars, so there is probably something I
just "don't get."

Fueleconomy.gov states that above 60 MPH, fuel economy drops
drastically. Does this depend on the engine type? For example, in my
car (94 Buick Regal, V6 3.8), when I compare Engine RPM at 55, 60, and
65 MPH, there is barely any difference. However, when I drive my mom's
01 Kia Sportage (4 Cylinder), the RPM difference is much larger. Does
this mean that my car's fuel economy isn't really affected until I start
going even faster, or is there some other thing that could be causing it?

Thanks,
Tom Varco

Wind resistance increases exponentially.

"Tom Varco" > wrote in message
news:d6KWd.70166$8a6.35201@trndny09...
> First off, I know nothing about cars, so there is probably something I
> just "don't get."
>
> Fueleconomy.gov states that above 60 MPH, fuel economy drops drastically.
> Does this depend on the engine type? For example, in my car (94 Buick
> Regal, V6 3.8), when I compare Engine RPM at 55, 60, and 65 MPH, there is
> barely any difference. However, when I drive my mom's 01 Kia Sportage (4
> Cylinder), the RPM difference is much larger. Does this mean that my
> car's fuel economy isn't really affected until I start going even faster,
> or is there some other thing that could be causing it?
>
> Thanks,
> Tom Varco

Tom Varco wrote:
>
> First off, I know nothing about cars, so there is probably something I
> just "don't get."
>
> Fueleconomy.gov states that above 60 MPH, fuel economy drops
> drastically. Does this depend on the engine type? For example, in my
> car (94 Buick Regal, V6 3.8), when I compare Engine RPM at 55, 60, and
> 65 MPH, there is barely any difference. However, when I drive my mom's
> 01 Kia Sportage (4 Cylinder), the RPM difference is much larger. Does
> this mean that my car's fuel economy isn't really affected until I start
> going even faster, or is there some other thing that could be causing it?
>
> Thanks,
> Tom Varco

Wind resistance.

"Tom Varco" wrote

> Fueleconomy.gov states that above 60 MPH, fuel economy drops
> drastically. Does this depend on the engine type?

Depends on engine, gear and car (aerodynamics, weight).
Although wind resistance rises with the square power of velocity,
you will also give your engine a higher load (open throttle),
which is better for fuel economy.
Small engines/cars which already have a nearly open throttle at 60mph
will suffer more than big ones (relativ to their minimum consumption).

Thomas

In article >, James C. Reeves wrote:
>Wind resistance increases exponentially.

No, as a square of velocity.

>"Tom Varco" > wrote in message
>news:d6KWd.70166$8a6.35201@trndny09...
>> First off, I know nothing about cars, so there is probably something I
>> just "don't get."
>>
>> Fueleconomy.gov states that above 60 MPH, fuel economy drops drastically.
>> Does this depend on the engine type? For example, in my car (94 Buick
>> Regal, V6 3.8), when I compare Engine RPM at 55, 60, and 65 MPH, there is
>> barely any difference. However, when I drive my mom's 01 Kia Sportage (4
>> Cylinder), the RPM difference is much larger. Does this mean that my
>> car's fuel economy isn't really affected until I start going even faster,
>> or is there some other thing that could be causing it?
>>
>> Thanks,
>> Tom Varco
>
>


--
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\ / http://charm.zag.si/eng/, email: "name dot surname AT zag dot si"
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Just for reference, "square of velocity" is the another way of saying
"exponentially" if the exponent is 2 so James is correct and so are you.

In reference to the original question. All engines also have an efficiency
curve so there is an rpm/load where the engine is most efficient. While it
takes less power to drive 50mph than 60, some cars are more efficient at 60
(use less fuel to make 1 hp) but keep in mind you need significantly more hp
at 60 as others have said.. I used to have Cougar with the 5.0 motor. At
60mph it only ran 1500 rpm and at 80 it ran 2000. No matter how I drove, it
almost always averaged 27mpg on the highway. So, I think the answer to your
question is "it depends"... Regarding the difference between your Regal and
Mom's Kia, the gearing is different due to the different sized motors and
their available torque and power..

"Jan Kalin" > wrote in message
...
> In article >, James C. Reeves wrote:
> >Wind resistance increases exponentially.
>
> No, as a square of velocity.
>
> >"Tom Varco" > wrote in message
> >news:d6KWd.70166$8a6.35201@trndny09...
> >> First off, I know nothing about cars, so there is probably something I
> >> just "don't get."
> >>
> >> Fueleconomy.gov states that above 60 MPH, fuel economy drops
drastically.
> >> Does this depend on the engine type? For example, in my car (94 Buick
> >> Regal, V6 3.8), when I compare Engine RPM at 55, 60, and 65 MPH, there
is
> >> barely any difference. However, when I drive my mom's 01 Kia Sportage
(4
> >> Cylinder), the RPM difference is much larger. Does this mean that my
> >> car's fuel economy isn't really affected until I start going even
faster,
> >> or is there some other thing that could be causing it?
> >>
> >> Thanks,
> >> Tom Varco
> >
> >
>
>
> --
> /"\ Jan Kalin (male, preferred languages: Slovene, English)
> \ / http://charm.zag.si/eng/, email: "name dot surname AT zag dot si"
> X ASCII ribbon campaign against HTML in mail and postings.
> / \ I'm a .signature virus. Copy me to help me spread.

"James C. Reeves" > wrote in message
...
> Wind resistance increases exponentially.
>
>>snip<<
...and so often forgotten/overlooked/didn't know in the 1st
place(me!).........but good to know & remember. s

In article >, bob wrote:
>Just for reference, "square of velocity" is the another way of saying
>"exponentially" if the exponent is 2 so James is correct and so are you.

No! An exponential function is of the form f(x) = a^x (i.e., some constant
raised to the power of x), whereas a power function is of the form f(x) =
x^b (i.e., x raised to the power of b). Totally different functions.

[SNIP]
>
>"Jan Kalin" > wrote in message
...
>> In article >, James C. Reeves wrote:
>> >Wind resistance increases exponentially.
>>
>> No, as a square of velocity.

--
/"\ Jan Kalin (male, preferred languages: Slovene, English)
\ / http://charm.zag.si/eng/, email: "name dot surname AT zag dot si"
X ASCII ribbon campaign against HTML in mail and postings.
/ \ I'm a .signature virus. Copy me to help me spread.

Tom Varco wrote:

> First off, I know nothing about cars, so there is probably something I
> just "don't get."
>
> Fueleconomy.gov states that above 60 MPH, fuel economy drops
> drastically. Does this depend on the engine type? For example, in my
> car (94 Buick Regal, V6 3.8), when I compare Engine RPM at 55, 60, and
> 65 MPH, there is barely any difference. However, when I drive my mom's
> 01 Kia Sportage (4 Cylinder), the RPM difference is much larger. Does
> this mean that my car's fuel economy isn't really affected until I start
> going even faster, or is there some other thing that could be causing it?
>
> Thanks,
> Tom Varco

No, it is a function of vehicle dynamics. Air drag becomes the most
important user of engine power at speeds above about 45-50 mph, unless
you are driving up a VERY steep hill.

Drag forces go as square of mph, power required as CUBE of mph, and fuel
consumption proportional to power. So at highway speeds a little bit of
speed increase takes a lot of fuel consumption increase.

Also, the statement was for constant speed- cruise conditions.
Acceleration takes fuel.

An often overlooked use of fuel is braking. People who use the brake a
lot use more fuel. Every btu of heat that comes from brakes ultimately
originates in fuel tank (except when you start your drive on top of a
mountain :-) ).

People who play traffic lights and coast to a stop burn significantly
less fuel than those who rush up to red lights and brake heavily.

bob wrote:

> Just for reference, "square of velocity" is the another way of saying
> "exponentially" if the exponent is 2 so James is correct and so are you.
>

It is another way, loosely. Yeah, the exponent is two, but some folks
who are math purists would say exponential means X raised to some
constant times e (base of natural logarithms). I personally am
comfortable with the original statement, though saying drag force
required goes as square and drag power as cube is a little more complete.