Re: Please check my Calculations
 

Caroline wrote:
> "L Alpert" <alpertl@xxcomcast.net> wrote in message
> news:B7Svc.39982$3x.16505@attbi_s54...
>> Caroline wrote:
>>> "yahmed" <ahmedyassir@yahoo.com> wrote
>>>> My accord'93 LX did 580KM (mixed highway and city) in 49L.
>>>>
>>>> So it comes to
>>>>
>>>> (49 % 3.785 = 12.94 US Gallons)
>>>
>>> 12.95, rounding off correctly...
>>>
>>>> (580 % 1.6093 = 360.4 Miles)
>>>>
>>>> 360.4 % 12.94 = 27.85 Miles/Gallon
>>>
>>> Let's call it 27.8 mpg.
>>
>> Actually, correct rounding would make this 27.9
>
> Not when you use the correct figure to four significant digits of
> 12.95.
>
>> (unless the 27.85 is rounded
>> up from something between 27.8-27.8499.......)
>
> Actually, both
>
> (580 / 1.6093) / (49 / 3.785) = 27.8, to the nearest tenth,
> rounding the final result correctly.
>
> and
>
> 360.4 / 12.95 = 27.8, to the nearest tenth, rounding the final result
> correctly
>
> If you want to get into the rules of significant digits rounding,
> feel free. But I suspect


Well, we could argue about what is least significant, but it would be a
useless exercise. As far as gas mileage is concerned, I would think a
single decimal place would be proper, as the error is small.

The 12.94, that would be rounded to 12.9, keeping it constant if it is
decided to use 3 significant digits, which would yield a 27.9 final tally.
Either way, both numbers are <.2% off from the 27.85 figure. This margin of
error could be deemed acceptable. Without having an actual tolerance, it is
impossible to tell what really is least significant.

Re: Please check my Calculations
 

J M wrote:
> the reason why the cut off is '5'....
>
> 0,1,2,3,4 round down (preceding digit is not advanced)
> 5,6,7,8,9 round up (preceding digit is advanced)
>
>
> which gives us an even split

No need to round a "0". It's already there.

>
>
>
> "Caroline" <caroline10027remove@earthlink.net> wrote in message
> news:qeTvc.1044$uX2.607@newsread2.news.pas.earthli nk.net...
>> "Misterbeets" <misterbeets@removehotmail.com> wrote
>>> I would like to get into those rules. What do you think of my
>>> practice of rounding numbers that end in 5: even numbers like 85 go
>>> down to 8; odd like 75 go up to 8. That way, on average, no bias is
>>> introduced.
>>
>> This is a test, right?
>>
>> 85 is not an even number. ;-)
>>
>> Otherwise, whether your rule is useful depends on your mathematical
>> goal.

Re: Please check my Calculations
 

"Cosmin N." <no@email.com> wrote in message
news:<zTUvc.16724$bVw1.8088@news01.bloor.is.net.ca ble.rogers.com>...

> 2. Go to www.google.com and type in the search box:
>
> 11.86km/l = ? miles/gallon
>
> The answer google returned was 27.89 miles/gallon which is very close to
> your result. The default in google is in US gallons, but you can specify
> Imperial (British) gallons as well.

Ah, good one, thanks. I'd used google's calculator a time or two for
simple expressions but didn't know it could accept equations. You've
prompted me to read a bit more about it, and it seems quite flexible.
From your example above,

11.86km/l=?mi/gal

and

11.86km/l in mi/gal

give the same result, and for example

32c=?f

or

32c in f

converts 32 degrees Centigrade into degrees Farenheit. But how do we
know which units are convertible? From

http://www.google.com/help/calculator.html

"The calculator understands many different units, as well as many
physical and mathematical constants. These can be used in your
expression. Many of these constants and units have both long and short
names. You can use either name in most cases. For example, km and
kilometer both work, as do c and the speed of light.

Feel free to experiment with the calculator as not all of its
capabilities are listed here."

Ha! Ah well, perhaps they'll add a units key soon. I'd been using

http://www.onlineconversion.com

but access to Google is quicker.

-------
NB: If response to this post does not concern the calculator, please
delete k12.ed.math and sci.math newsgroups from your post, thanks.

(Mutter, mutter, now lessee, 2 mi = ? nautical miles...ah, works.
Hmm, what about deg-min-sec to UTM...)

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Re: Please check my Calculations
 

1000 meters will cut your horsepower output by 11%. I lived at 3000
feet for 5 years and that was the concensus in the automotive world
there. Atmospheric O2 pressure is essentially a logarithmic function
of the altitude, so it is not proportional and you can't "eyeball" the
power loss at other altitudes using this figure.

The altitude will not directly affect your mileage, at least on modern
FI cars. But, since you have to rev the engine harder to keep up
decent torque, there will be small additional friction losses due to
the higher rpm. Also its harder on your ears to drive this way, so
maybe some people will settle for lower engine output in the first
place.

JM

Re: Please check my Calculations
 

Indirecto wrote:

> My 2004 Accord EX (4-cyl), auto is doing little more than 8k/liter, or about
> 20mpg... all city driving. It has about 4500 Km in the odometer (about 2800
> miles).
>
> I recall it doing about 11.5 k/l, or about 27mpg on pure highway driving.
>
> I wonder how Honda got the Accord can do 34mpg...

IIRC Honda didn't get that, the EPA did. Overall my '03 Accord EX sedan
w/automatic has gotten 26 mpg (12,500 miles). I consistently get > 30
mph on the highway, with a max going to NC of 34 mpg (absolutely NO city
driving & no A/C).

Re: Please check my Calculations
 

You are getting terrible mileage out of your 04 Accord. 8km/l (or
12.5litres/100km) is 18 mpg, which is far below the fuel efficiency of
an Accord 4-cyl.

My 01 Prelude (which is far less fuel efficient than a 04 Accord)
consumes about 11 litres/100km (21.4mpg), in city driving. On the
highway I am getting about 9 litres/100km (26.1mpg). My old 94 Accord
EXR was getting slightly better numbers than my 01 Prelude.

So there is either something wrong with your car, or you are a very
agressive driver.

Cosmin

Indirecto wrote:

> My 2004 Accord EX (4-cyl), auto is doing little more than 8k/liter, or about
> 20mpg... all city driving. It has about 4500 Km in the odometer (about 2800
> miles).
>
> I recall it doing about 11.5 k/l, or about 27mpg on pure highway driving.
>
> I wonder how Honda got the Accord can do 34mpg...
>
> -Indirecto
>
>
>
> "yahmed" <ahmedyassir@yahoo.com> wrote in message
> news:9b1229.0406030802.2d2d9567@posting.google.com ...
>
>>Hi,
>>
>>My accord'93 LX did 580KM (mixed highway and city) in 49L.
>>
>>So it comes to
>>
>>(49 % 3.785 = 12.94 US Gallons)
>>(580 % 1.6093 = 360.4 Miles)
>>
>>360.4 % 12.94 = 27.85 Miles/Gallon
>>
>>
>>Is this good?
>>
>>(It has 195K KM on it and I recently had it tuned.)
>>
>>Thanks.
>
>
>

Re: Please check my Calculations
 

"JM" <jmattis@attglobal.net> wrote
> 1000 meters will cut your horsepower output by 11%. I lived at 3000
> feet for 5 years and that was the concensus in the automotive world
> there.

What I'm seeing generally supports this. For the interested car enthusiast, see
for example:

1.
http://wahiduddin.net/calc/calc_hp_dp.htm and
http://wahiduddin.net/calc/cf.htm, along with the pointers from these sites.

2.
"The correlation between altitude and power goes like this: a gasoline engine
loses three percent of its horsepower output for every thousand feet of
altitude, a function of relative oxygen scarcity as the altimeter needle
climbs."
http://www.caranddriver.com/article....rticle_id=8074 But again,
this was for racing cars, presumably operating at maximum possible horsepower.

> Atmospheric O2 pressure is essentially a logarithmic function
> of the altitude,

For the same temperatue and relative humidity but two different altitudes, air
pressure varies very close to perfectly inversely with altitude, at least for
altitudes from sea level to 15,000 feet. I believe the percent oxygen that air
contains is fairly fixed with altitude (again, assuming constant temperature and
relative humidity).

> so it is not proportional and you can't "eyeball" the
> power loss at other altitudes using this figure.

After experimenting with the numbers and calculator above, the 3% hp lost/1000
feet of altitude appears to me to be a "not bad" rule of thumb.

> The altitude will not directly affect your mileage, at least on modern
> FI cars. But, since you have to rev the engine harder to keep up
> decent torque, there will be small additional friction losses due to
> the higher rpm.

So small as to be negligible, at least for my move from sea level to a mile
high.

> Also its harder on your ears to drive this way, so
> maybe some people will settle for lower engine output in the first
> place.

Re: Please check my Calculations
 

Thanks,

I am a fairly aggressive driver (not that much, tho), and the kind of
driving is pure stop & go. Absolutely no highway. (Not a good combo).

I tried "premium" gas to see if it helped. It didn't, so I am back to
regular now.

Still, I'll talk to the dealer when it goes to its 5000K checkup.

-Indirecto


"Cosmin N." <no@email.com> wrote in message
news:O%dwc.26966$bVw1.2217@news01.bloor.is.net.cab le.rogers.com...
> You are getting terrible mileage out of your 04 Accord. 8km/l (or
> 12.5litres/100km) is 18 mpg, which is far below the fuel efficiency of
> an Accord 4-cyl.
>
> My 01 Prelude (which is far less fuel efficient than a 04 Accord)
> consumes about 11 litres/100km (21.4mpg), in city driving. On the
> highway I am getting about 9 litres/100km (26.1mpg). My old 94 Accord
> EXR was getting slightly better numbers than my 01 Prelude.
>
> So there is either something wrong with your car, or you are a very
> agressive driver.
>
> Cosmin
>
> Indirecto wrote:
>
> > My 2004 Accord EX (4-cyl), auto is doing little more than 8k/liter, or
about
> > 20mpg... all city driving. It has about 4500 Km in the odometer (about
2800
> > miles).
> >
> > I recall it doing about 11.5 k/l, or about 27mpg on pure highway
driving.
> >
> > I wonder how Honda got the Accord can do 34mpg...
> >
> > -Indirecto
> >
> >
> >
> > "yahmed" <ahmedyassir@yahoo.com> wrote in message
> > news:9b1229.0406030802.2d2d9567@posting.google.com ...
> >
> >>Hi,
> >>
> >>My accord'93 LX did 580KM (mixed highway and city) in 49L.
> >>
> >>So it comes to
> >>
> >>(49 % 3.785 = 12.94 US Gallons)
> >>(580 % 1.6093 = 360.4 Miles)
> >>
> >>360.4 % 12.94 = 27.85 Miles/Gallon
> >>
> >>
> >>Is this good?
> >>
> >>(It has 195K KM on it and I recently had it tuned.)
> >>
> >>Thanks.
> >
> >
> >

Re: Please check my Calculations
 

OK, I looked at this further, & at meaningful automotive altitudes I
agree you can loosly approximate it at 3% per thousand feet. It has a
much bigger effect at higher altitudes. My bad.

JM

Re: Please check my Calculations
 

"JM" <jmattis@attglobal.net> wrote
> OK, I looked at this further, & at meaningful automotive altitudes I
> agree you can loosly approximate it at 3% per thousand feet. It has a
> much bigger effect at higher altitudes. My bad.

Hey, no bad. I didn't think anything meaningful happened at high altitudes. On
the contrary, your first observation about the consensus where you live being
"hp lost is about 11% at 3000 feet" is a great guideline.

I figure most folks who have any Western mountain driving experience know the HP
is going to get worse--but not unmanageable--at the usual driving higher
altitudes. It's better at lower altitudes. So it seems a bit intuitive that HP
variation with altitude is very crudely (but still usefully) linear.

Shoulda figured this from my summer running a little cross-country near Boulder,
Colorado.