Best MPG : 5-speed vs. auto?

Assuming an identical car, let's say a 4-cyl Honda or a Subaru or
Toyota, which would
get better MPG -- one with automatic tranny or 5-speed?

I understand that 5 speeds vs. 4 gives a better selection of rpms,
meaning at the same speed you can cruise with lower rpms, assuming the
same rear axle ratio.

Also I understand that 5-speeds don't have a torque converter that
autos have which robbs some power.

But in my experience, in city driving, it's hard to shift well for good
MPG. Maybe I am shifting at wrong rpms, I am not sure.

SQ wrote:
>
> Assuming an identical car, let's say a 4-cyl Honda or a Subaru or
> Toyota, which would
> get better MPG -- one with automatic tranny or 5-speed?
>
> I understand that 5 speeds vs. 4 gives a better selection of rpms,
> meaning at the same speed you can cruise with lower rpms, assuming the
> same rear axle ratio.
>
> Also I understand that 5-speeds don't have a torque converter that
> autos have which robbs some power.
>
> But in my experience, in city driving, it's hard to shift well for good
> MPG. Maybe I am shifting at wrong rpms, I am not sure.

Automatics will always have some loss due to the torque convertor.
However, they tend to be equal to sticks because most drivers are not good
shifters.
If you want good mileage, then shift at the lowest rpm possible without lugging
and drive as slow as possible without getting shot.
I don't know you mean about "5-speeds don't have a torque converter".
Are you speaking of automatics, or sticks, or something bizarre like a
convertor-less double clutch automatic?

Well, this explains a lot. I have been driving a 5-speed and have been
getting awful mpg in city. Now I am realizing I am shifting at very
high rpms, around 2500. I will try to lower the rpms during shifting
and see if it makes any difference.

(I think one problem in my particular situation is that the type of
engine I have derives it's power from high rpms, you have to rev it to
get going, and I don't like it)

SQ wrote:
>
> Well, this explains a lot. I have been driving a 5-speed and have been
> getting awful mpg in city. Now I am realizing I am shifting at very
> high rpms, around 2500. I will try to lower the rpms during shifting
> and see if it makes any difference.
>
> (I think one problem in my particular situation is that the type of
> engine I have derives it's power from high rpms, you have to rev it to
> get going, and I don't like it)

Small overhead cam engines are like that. Especially ones with lots of valves per
cylinder. They develop max hp and torque near max rpm.

« Paul » wrote:
> SQ wrote:
>
>>Well, this explains a lot. I have been driving a 5-speed and have been
>>getting awful mpg in city. Now I am realizing I am shifting at very
>>high rpms, around 2500. I will try to lower the rpms during shifting
>>and see if it makes any difference.
>>
>>(I think one problem in my particular situation is that the type of
>>engine I have derives it's power from high rpms, you have to rev it to
>>get going, and I don't like it)
>
>
> Small overhead cam engines are like that. Especially ones with lots of valves per
> cylinder. They develop max hp and torque near max rpm.

But you don't NEED that much hp to drive it. One can take off with fair
throttle, as soon as you are moving, begin shifting. Short shift. You
will not be the leader of the pack, but you can save gas.

"SQ" > wrote in message
oups.com...
>
> Well, this explains a lot. I have been driving a 5-speed and have been
> getting awful mpg in city. Now I am realizing I am shifting at very
> high rpms, around 2500. I will try to lower the rpms during shifting
> and see if it makes any difference.
>
> (I think one problem in my particular situation is that the type of
> engine I have derives it's power from high rpms, you have to rev it to
> get going, and I don't like it)

As he said, the automatic should have a little more loss, but in fact they
get about
as good mileage as manuals for most drivers.

Drive as though you have a glass of water sitting on the dash. Hi revs
usually
waste fuel. Jump starts, race car tactics usually waste.

On 8 Apr 2006 15:32:49 -0700, "SQ" > wrote:

>
>Well, this explains a lot. I have been driving a 5-speed and have been
>getting awful mpg in city. Now I am realizing I am shifting at very
>high rpms, around 2500.

I can't think of anything other than a large diesel engine where 2500
rpm could be considered "high" let alone "very high." If its a 4 cyl
OHC engine its just barely entering the bottom of its power band at
2500. "Very high" rpms would be more in the range 0f 7000-8000. Many
modern totally stock 4 cyl. engines can handle that with no ill
effects whatsoever.

> I will try to lower the rpms during shifting
>and see if it makes any difference.
>
>(I think one problem in my particular situation is that the type of
>engine I have derives it's power from high rpms, you have to rev it to
>get going, and I don't like it)

Then you should buy an old Lincoln or 500 cubic inch Cadillac
Eldorado. Small engines all need to rev to produce power.

FWIW automatic transmissions free-wheel under various conditions which
helps offset their gas mileage reducing attributes. Its easy to see
this if you have a tach.

Don
www.donsautomotive.com

« Paul » <"« Paul > wrote in article
>...
> SQ wrote:
> >
> > Assuming an identical car, let's say a 4-cyl Honda or a Subaru or
> > Toyota, which would
> > get better MPG -- one with automatic tranny or 5-speed?
> >
> > I understand that 5 speeds vs. 4 gives a better selection of rpms,
> > meaning at the same speed you can cruise with lower rpms, assuming the
> > same rear axle ratio.
> >
> > Also I understand that 5-speeds don't have a torque converter that
> > autos have which robbs some power.
> >
> > But in my experience, in city driving, it's hard to shift well for good
> > MPG. Maybe I am shifting at wrong rpms, I am not sure.
>
> Automatics will always have some loss due to the torque convertor.



The use of lock-up torque converters has eliminated that situation.

When the converter is locked, you have a direct mechanical connection
between the engine crankshaft and the driveshaft - just as with a manual
tranny.

Computer-controlled transmissions can now shift gears at exactly the
correct moment......

If it is fuel mileage I'm looking for, I'll take an automatic over a stick.

* wrote:
>
> Computer-controlled transmissions can now shift gears at exactly the
> correct moment......
>
> If it is fuel mileage I'm looking for, I'll take an automatic over a stick.
>
>
>

No way! We traded in a Voyager stick for a new Chrysler van. The auto
in the new one shifts at WAY higher rpm than we did with the old one,
and we get nowhere the milage. You can short shift a stick- newer ones
with computer control, you can't even FORCE an upshift! And the
computer wants to supply AVERAGE driving program. If I knew how to redo
programming I would.

Anyone know if the dealer shop can alter the shift point?

"Don Stauffer" > wrote in message
...
> * wrote:
> >
> > Computer-controlled transmissions can now shift gears at exactly the
> > correct moment......
> >
> > If it is fuel mileage I'm looking for, I'll take an automatic over a
stick.
> >
> >
> >
>
> No way! We traded in a Voyager stick for a new Chrysler van. The auto
> in the new one shifts at WAY higher rpm than we did with the old one,
> and we get nowhere the milage. You can short shift a stick- newer ones
> with computer control, you can't even FORCE an upshift! And the
> computer wants to supply AVERAGE driving program. If I knew how to redo
> programming I would.
>
> Anyone know if the dealer shop can alter the shift point?

Most Chrysler minivan sticks were on the short wheelbase 2.5L you have
a 3.8L in a long wheelbase there now that weighs a hell of a lot more.
If you had a stick on there you would get even worse mileage.

Ted