Prev: Suggestions from your experience organizing metric & englishc...
Next: anyone have an old Trico catalog?
From: Jesse on 8 Jul 2010 10:51
On Thu, 8 Jul 2010 14:39:48 +0800, "TE Cheah" <4ws(a)gmail.com> wrote:

>> Would a 6 Cylinder at 65 MPH showing 2200 RPM use less fuel than a 4
>> cylinder showing 2600 RPM at 65 MPH?
>
>If this 6 cyl has 3 litre, then 3 x 4/6 x 26/22 = 2363 cc, so if this
>4 cyl has >2363cc, both have same fuel ratio @ these rpm, no
>super / turbo charging, then theoretically this 4 cyl will use more.
>
Thanks everyone, I'll give this up. I hoped that there was some
correlation of mpg to rpm.
From: Scott Dorsey on 8 Jul 2010 11:00
Jesse <sumin(a)telus.net> wrote:
>On Thu, 8 Jul 2010 14:39:48 +0800, "TE Cheah" <4ws(a)gmail.com> wrote:
>
>>> Would a 6 Cylinder at 65 MPH showing 2200 RPM use less fuel than a 4
>>> cylinder showing 2600 RPM at 65 MPH?
>>
>>If this 6 cyl has 3 litre, then 3 x 4/6 x 26/22 = 2363 cc, so if this
>>4 cyl has >2363cc, both have same fuel ratio @ these rpm, no
>>super / turbo charging, then theoretically this 4 cyl will use more.
>>
>Thanks everyone, I'll give this up. I hoped that there was some
>correlation of mpg to rpm.

Why would there be?

Every time the engine goes around, it sucks in some amount of fuel
proportional to the displacement and the throttle. Every time the engine
goes around, it moves the car forward some amount proportional to the
transmission and differential gearing.

So... if you knew the displacement and you knew the throttle percentage
and you knew the transmission and differential ratios, you could figure
the mpg at any point in time. However, the throttle percentage is something
that changes a lot as you drive.

And one big hint: the lighter a car is, the less throttle you need to make
it accelerate. The lighter car will almost invariably have the best mileage,
in the long run.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
From: hls on 8 Jul 2010 17:26

"Jesse" <sumin(a)telus.net> wrote in message
>
> Perhaps I should clarift my situation. The discussion followed an
> attempt to select a car for my daughter, she prefers good milage. I
> drove both cars on the same road, at the same speed and observed at 65
> MPH the 4 cyl at 2700 rpm and the 6 cyl at 2200 rpm. The question was
> which car should get the best fuel economy at these conditions.
> Neither myfriend or I know.

There is not enough data to make a definitive selection. BUT, I have
seen some of these four cylinders that run higher RPM's, as you mentioned,
get terrible mileage. Part of that equation is transmission and gearing,
BUT
if you have an anemic little four you may find you are in the accelerator
too much, trying to make a hill or trying to pass something, and it can
be an unpleasant event, both from driving satisfaction and from economy.

My father-on-law has a 2.3 litre Jimmy pickup that has no power, is not
at all pleasant to drive, and has never gotten 20 mpg in its life

I drove a 4 cylinder Honda before I bought Toyota, and it was a gutless
little machine (to me).

A well set up 6 cylinder can get very good mileage, and can be a heck of a
lot more driveable on the highway. For example, my old Buick Regal (89)
had the 2.8 litre V6, and always got 35 mpg on the highways. Other than
that, it was a pleasure to drive, but one of the most fragile, undependable
turdcars I have ever seen.

You can look at the estimated mileage figures for each car, but those may
be off a good bit.

Our 268 hp Avalon will average 32 mpg on the highwar. And it has great
power for when you really need power.

Look at the mileage, certainly, but look a little further befure you buy her
a car.

From: hls on 8 Jul 2010 17:28

"Jesse" <sumin(a)telus.net> wrote in message
>>
> Thanks everyone, I'll give this up. I hoped that there was some
> correlation of mpg to rpm.

No, there isnt. For your daughter, you want something very dependable,
with reasonably good mileage, that handles well and can keep her relatively
safe.

I suggest you forget the mpg to rpm ratios.
From: TE Cheah on 9 Jul 2010 06:29
> you knew the throttle percentage
How does she know this when driving ? 1 can feel how far 1
depresses throttle pedal, but the only accurate way to know how
far throttle opens is to connect a wire to TPS's output & see
voltage ( e.g. 0.5v when closed, 4.44v when fully open, on my
F20A ).

> you could figure the mpg at any point in time.
How ?


First  |  Prev  |  Next  |  Last
Pages: 1 2 3 4 5 6
Prev: Suggestions from your experience organizing metric & englishc...
Next: anyone have an old Trico catalog?