A modest fuel saving proposal: no more than 3000 RPM

Some have already posted about bringing back the 55mph speed limit, but
obviously, that's not very practical nowadays with today's modern vehicles.

My proposal--though I admit that my only data point at the present time is
the fuel efficiency of my own vehicle--is not to exceed 3000 RPM in any
particular gear, including the topmost gear of a manual or automatic
transmission equipped vehicle.

As far as freeway speeds were concerned in the topmost gear (4th gear of a 4
speed automatic overdrive transmission), I noted that 2500 RPM was just a
bit under 65mph, while 3000 RPM was around 75mph but not quite 80mph.
Transmissions with higher gears may have a greater top speed even when
keeping at or below 3000 RPM, but for now, I'm setting aside the speed limit
issues in favor of discussing fuel economy.

Obviously, there will be some occasions where it may be necessary to exceed
3000 RPM, such as driving up a grade, but for the most part, my proposal
applies to most surface streets and freeways that are on reasonably level
ground.

Hopefully, there will be some reasonable discussion about this proposal and
not just knee-jerk flames.

"Daniel W. Rouse Jr." > wrote in message
...
> Some have already posted about bringing back the 55mph speed limit, but
> obviously, that's not very practical nowadays with today's modern
vehicles.
>
> My proposal--though I admit that my only data point at the present time is
> the fuel efficiency of my own vehicle--is not to exceed 3000 RPM in any
> particular gear, including the topmost gear of a manual or automatic
> transmission equipped vehicle.
>


That wouldn't work for all vehicles. My own vehicle does about 3500RPM on
the highway, at roughly 78MPH and 42MPG. If I drop to below 3000 RPM
(slowed by traffic, too many cops around, etc.), I'm lucky (very lucky) to
hit 35MPG.

While I haven't always paid close attention to RPM, I have noticed that a
few vehicles (including my current one) I have owned in my lifetime had a
sweet spot (for the engine) that would greatly increase fuel economy. In
all the vehicles I have observed this, that maximum fuel economy point was
somewhere over 70MPH. In all cases, the best fuel economy was achieved
while the engine was running (relatively) high RPM.

Whether you think of it as limiting speed (like say a 55MPH speed limit) or
limiting RPM (like say a 3000RPM upper limit), either way could BACKFIRE on
you, if you are trying to save fuel. For your car, it might work. I've
already observed that my own car uses more fuel below 3000 than it does
around 3500.

If you want to know why some cars get better fuel economy at slightly higher
engine RPM, look no further than the brochure used by car dealers to sell
your particular car. Just about all of them have horsepower and torque
ratings listed for a corresponding engine RPM range. You'll note that most
engines need to be running at a rather high RPM to run MOST efficiently,
though some of them also offer lots of "low-end" torque. In other words, if
you want the best performance out of your engine, MOST of them will need to
be run a bit closer to (redline) than (idle). The sweet spot for many cars
seems to be somewhat above the halfway point. Or if your redline is 6000,
the maximum fuel economy might be somewhere above 3000. Much faster OR
slower, the engine will be working harder, burning fuel faster. -Dave

> If you want to know why some cars get better fuel economy at slightly higher
> engine RPM, look no further than the brochure used by car dealers to sell
> your particular car. Just about all of them have horsepower and torque
> ratings listed for a corresponding engine RPM range.

How can you explain this to people who repeat the old mantra - "Slow
down if you want to save fuel." They won't look at a graph or the data
for efficiency ratings.

"Daniel W. Rouse Jr." wrote:

> Some have already posted about bringing back the 55mph speed limit, but
> obviously, that's not very practical nowadays with today's modern vehicles.

What *exactly* is impractical about it ? Is your right foot so heavy that you
can't drive at that speed ?

BTW, I wouldn't *like* to see a 55mph limit actually. The need would be removed
if ppl drove more fuel efficent cars ( instead of their personal armed personnel
carriers ) though.

Graham

Alexander Rogge wrote:

> > If you want to know why some cars get better fuel economy at slightly higher
> > engine RPM, look no further than the brochure used by car dealers to sell
> > your particular car. Just about all of them have horsepower and torque
> > ratings listed for a corresponding engine RPM range.
>
> How can you explain this to people who repeat the old mantra - "Slow
> down if you want to save fuel." They won't look at a graph or the data
> for efficiency ratings.

How can you explain *anything* to ppl with such a narrow viewpoint ?

One of the best ways to save fuel btw is to drive at a speed that avoids regular
use of the brake. That speed wil vary according to the road and driving
conditions. Constant acceleration and deceleration is highly wasteful of fuel.

Graham

>> If you want to know why some cars get better fuel economy at slightly
>> higher
>> engine RPM, look no further than the brochure used by car dealers to sell
>> your particular car. Just about all of them have horsepower and torque
>> ratings listed for a corresponding engine RPM range.
>
> How can you explain this to people who repeat the old mantra - "Slow down
> if you want to save fuel." They won't look at a graph or the data for
> efficiency ratings.

Simple. Well, it WAS simple before gas was twenty bucks a gallon.

I'd tell them to try it themselves. Take a trip of mostly uncongested
highway miles greater than 200. Try to keep your speed at 55 (tough I know,
but try). Measure your mileage, preferably round trip.

Then later, repeat the same trip at 70 or higher. If you're a good driver,
let the car pick its own speed (just watch out for the cops, obviously).
Most cars when nicely warmed up seem to settle into a comfortable cruising
speed somewhere around 70 or so. If you can 'feel' where this comfortable
cruising speed is, that's probably close to the engine's sweet spot.
Measure your mileage again.

Be prepared to be surprised, as most of you will probably get significantly
better gas mileage at higher average speeds (within reason, obviously . . .
don't expect 120 to be better than 60, as 120 would put your engine too far
out of its maximum efficiency range, also)

If people would just do this (and assuming they knew how to calculate gas
mileage correctly), there would be no explanation necessary. BUT, for those
who want it, I'd again refer them to the brochure used to sell their car.
Once they've seen the actual fuel savings at slightly higher speeds, the
graphs and data on engine horsepower/torque/RPM will make more sense.
Because they will probably have a good idea where the "sweet spot" of their
engine is already, and (not coincidentally) the graph/data will likely show
that the engine is producing a good amount of horsepower and/or torque at
that point. -Dave

Daniel W. Rouse Jr. wrote:
> Some have already posted about bringing back the 55mph speed limit, but
> obviously, that's not very practical nowadays with today's modern vehicles.
>
> My proposal--though I admit that my only data point at the present time is
> the fuel efficiency of my own vehicle--is not to exceed 3000 RPM in any
> particular gear, including the topmost gear of a manual or automatic
> transmission equipped vehicle.
>
> As far as freeway speeds were concerned in the topmost gear (4th gear of a 4
> speed automatic overdrive transmission), I noted that 2500 RPM was just a
> bit under 65mph, while 3000 RPM was around 75mph but not quite 80mph.
> Transmissions with higher gears may have a greater top speed even when
> keeping at or below 3000 RPM, but for now, I'm setting aside the speed limit
> issues in favor of discussing fuel economy.
>
> Obviously, there will be some occasions where it may be necessary to exceed
> 3000 RPM, such as driving up a grade, but for the most part, my proposal
> applies to most surface streets and freeways that are on reasonably level
> ground.
>
> Hopefully, there will be some reasonable discussion about this proposal and
> not just knee-jerk flames.

My personal vehicle is a Porsche 944; if I couldn't exceed 3000 RPM I
wouldn't ever be able to upshift. The engine just flat won't run
(well, it will, but it will let you know in no uncertain terms that
it's unhappy) under 2000 RPM.

I still get better gas mileage than the average SUV pilot and have a
hell of a lot more fun doing it. And I didn't pay $40K for my car
either.

nate

Dave C. wrote:
> "Daniel W. Rouse Jr." > wrote in message
> ...
>> Some have already posted about bringing back the 55mph speed limit,
>> but obviously, that's not very practical nowadays with today's
>> modern vehicles.
>>
>> My proposal--though I admit that my only data point at the present
>> time is the fuel efficiency of my own vehicle--is not to exceed 3000
>> RPM in any particular gear, including the topmost gear of a manual
>> or automatic transmission equipped vehicle.
>>
>
>
> That wouldn't work for all vehicles. My own vehicle does about
> 3500RPM on the highway, at roughly 78MPH and 42MPG. If I drop to
> below 3000 RPM (slowed by traffic, too many cops around, etc.), I'm
> lucky (very lucky) to hit 35MPG.
>

What car (a) gets 42mpg @78, and (b) is so horribly designed that it's
geared such that the efficient point of the engine RPM is at such an
incredibly high speed?

Imagine what your mileage would be if it were properly geared for 3500 rpm @
65. Remember energy to overcome wind resistance is exponential. I'd head
to the tranny shop today if it were my car! (somehow I think you are
stretching facts a tad)

> obviously). Most cars when nicely warmed up seem to settle into a
> comfortable cruising speed somewhere around 70 or so. If you can
> 'feel' where this comfortable cruising speed is, that's probably
> close to the engine's sweet spot.

ROTFL

On Thu, 1 Sep 2005, Daniel W. Rouse Jr. wrote:

> My proposal is not to exceed 3000 RPM in any particular gear, including
> the topmost gear of a manual or automatic transmission equipped vehicle.
> Hopefully, there will be some reasonable discussion about this proposal
> and not just knee-jerk flames.

What makes you expect more than your halfassed, ignorant idea deserves?