Interesting MPG experiment

[Rick Courtright]

People look at the STi I drive, and I know for a fact they're rooting for me
to crash.

Hi,

Yeah, of course they are! Learn to drive and I'll bet you find yourself
in far fewer of these "situations." People "root for crashes" at NASCAR
races... on the road, it ain't no race.

I see quite a few "wannabe racers" (sadly for the marque, more than a
few are driving WRXes and STis) on the road, and generally give them
plenty of room. Why? Experience and observation tells me their drivers
are far more likely to try to use their right foot instead of their
brain to manuever thru tricky situations. The only "tragedy" when such
drivers crash is that innocent people may be hurt. Otherwise, it's just
Darwin having his jollies.

Or, to quote a local traffic helicopter pilot, "I see a LOT of crashes
every day. I DON'T see many 'accidents.'"

DUUUUUDE!

Rick

 

[John O]

Hi,

Yeah, of course they are! Learn to drive and I'll bet you find yourself
in far fewer of these "situations." People "root for crashes" at NASCAR
races... on the road, it ain't no race.

I see quite a few "wannabe racers" (sadly for the marque, more than a
few are driving WRXes and STis) on the road, and generally give them
plenty of room. Why? Experience and observation tells me their drivers
are far more likely to try to use their right foot instead of their
brain to manuever thru tricky situations.

I see a lot of them too. I've taught my kids to watch for this special kind
of moron and give them space. Most of them seem to think they're still
playing a rally game on their X-Box.

-John O

 

[clare at snyder dot ontario dot canada]

I see a lot of them too. I've taught my kids to watch for this special kind
of moron and give them space. Most of them seem to think they're still
playing a rally game on their X-Box.

-John O

And most of them would not last very long in the "real world" of
rallying, either.
Posers and wannabees.
AKA aggressive drivers, AKA idiots.

 

[JD]

in message

The optimum engine speed for fuel economy is the maximum torque RPM.
That said,today's engines are VERY flexible that way. Maximum torque
goes from something like 1800 to 3000 rpm on some current engines.
My 2003 PT cruiser is not one of those - max torque is at 4000 RPM
and max HP at 5600. NO WAY that vehicle will be run at 4000 RPM cruise
The 2.5 liter duratec in my wife's Mystique produces the same peak
torque at 4200 rpm - but the torque curve is a lot fatter with the
variable intake geometry.

Not so. At peak torque the engine is using a great deal of fuel. I have an
04 STi. At 4000 RPM (its peak torque) it is burning fuel at 60 litres/hr at
100% load, and 20 litres/hr at light loading. Its best gas mileage is at
about 80 km/hr where it burns 7.2 litres/hr. That works out to about 31 MPG
(imperial gallons). I have hooked up the monitor to my wife's Forester as
well. Although the differences are not as great, her car still gets it best
mileage at around 80-85 km/hr.

 

[clare at snyder dot ontario dot canada]

in message


Not so. At peak torque the engine is using a great deal of fuel. I have an
04 STi. At 4000 RPM (its peak torque) it is burning fuel at 60 litres/hr at
100% load, and 20 litres/hr at light loading. Its best gas mileage is at
about 80 km/hr where it burns 7.2 litres/hr. That works out to about 31 MPG
(imperial gallons). I have hooked up the monitor to my wife's Forester as
well. Although the differences are not as great, her car still gets it best
mileage at around 80-85 km/hr.

The engine produces maximum hp/hr per lb of fuel at maximum torque
rpm. This is a well known proven fact. Now running it at full load at
this speed is a different story all together. The gearing is not
necessarily set up to provide maximum fuel economy at this speed on
the road - onn an STi I can almost guantee it is not - it is geared
for PERFORMANCE.

 

[YKhan]

My 2000 OBW usually gets shifted to 5th when I reach about 80kph
(50mph), until then 4th is the gear I can sustain it at. It really
doesn't matter when you shift into 5th or 4th, as long as you stay
below a certain RPM, you're doing fine. I usually use 3000RPM as my
rule of thumb. On my OBW @ 100kph (60mph), it reaches exactly 3000RPM
in 5th. This seems to be the sweet spot right now.

Yousuf Khan

 

[YKhan]

Now if I could just convince the guys who designed the "brain" behind
the one auto I own of that fact, instead of the trans constantly
"hunting" from 35-40 mph and up, trying to decide whether it should be
in 3rd, 4th or 5th! Doesn't save any gas, does tear up transmissions.
Oh, well...

I think you want a CVT.

Yousuf Khan

 

[John O]

The engine produces maximum hp/hr per lb of fuel at maximum torque
rpm. This is a well known proven fact. Now running it at full load at
this speed is a different story all together.

Wind is a full load for any vehicle, and without considering it the numbers
are meaningless. Take a test drive and try it...my OBW does about 30 mpg if
I drive at 64 mph on a trip....as slow as I can safely drive on the highways
here. At 70 mph, I get about 27 mpg. At 80, about 23. All cars have the
about the same curve, even your STi.

The *only* way you get better mileage at 80 mph is if you drive a
torpedo-shaped car, which has no wind resistance, and the STi doesn't
qualify. That's a proven fact, too.

-John O

 

[clare at snyder dot ontario dot canada]

Wind is a full load for any vehicle, and without considering it the numbers
are meaningless. Take a test drive and try it...my OBW does about 30 mpg if
I drive at 64 mph on a trip....as slow as I can safely drive on the highways
here. At 70 mph, I get about 27 mpg. At 80, about 23. All cars have the
about the same curve, even your STi.

The *only* way you get better mileage at 80 mph is if you drive a
torpedo-shaped car, which has no wind resistance, and the STi doesn't
qualify. That's a proven fact, too.

-John O

I've tried it - many times . It works. The 1975 Celica did over 50MPG
in fifth gear at about 80MPH, which had the engine at it's torque
peak. At 60 it would not do 40MPG, in any gear.
In 1976 they changed the gear ratio, and 50MPG was impossible.
Otherwise, the vehicle was virtually identical.
The aerodynamics on the GT fastback were pretty good. No Soob has
aerodynamics - particularly the ones with the boy-racer scoops and
tails.

 

[John O]

I've tried it - many times . It works.

You're saying that you violate the laws of thermodynamics, and you just
can't do that.

-John O

 

[JD]

You're saying that you violate the laws of thermodynamics, and you just
can't do that.

-John O

I agree. By 80 MPH a very high proportion of the work done by the engine is
lost to drag in any car.

 

[JD]

in message

The engine produces maximum hp/hr per lb of fuel at maximum torque
rpm. This is a well known proven fact. Now running it at full load at
this speed is a different story all together. The gearing is not
necessarily set up to provide maximum fuel economy at this speed on
the road - onn an STi I can almost guantee it is not - it is geared
for PERFORMANCE.

It is not a proven fact. You are thinking of thermal efficiency. You are
completely disregarding drag which is a very much more significant factor.
The thermal efficiency of a modern gas engine is between 25% and 30%. To
put that in layman's terms, every 100 gals you burn, only 25-30 is actually
converted to work. The rest is lost to heat. So, yes, it has its best
thermal efficiency at peak torque. However, the efficiency does not drop
significantly unless the engine is chugging at the lower end (incomplete
fuel burn) or pinging at the other end (predetonation). Everywhere else,
drag is the most important factor for the fuel economy of a car. At low
speed, most of the work the engine is doing is translated into movement of
the car. As speed increases, drag increases exponentially, and so does the
percentage of work used to overcome drag. At 40 MPH, about 10% of the work
the engine is doing is to overcome drag. By 55 MPH about 30% the work the
engine is doing is to overcome the drag. By 80 MPH, its more like 65%. by
100 MPH, it is like 90%.

An STi, at peak torque in 6th gear, is doing nearly 100 MPH. At that speed
gas mileage would seriously suck.

 

[clare at snyder dot ontario dot canada]

You're saying that you violate the laws of thermodynamics, and you just
can't do that.

-John O

Not violating the rules of thermodynamics.
And back the beginning of June I drove my PT cruiser 300 miles at
62MPH kph and got 34 MPG (Canadian)(waterloo to Barrie and back plus a
couple short trips) A couple weeks ago I did it again (waterloo to
Windsor- 60-62MPH and 300 miles, 34MPG. ANd the return trip, at the
same speed, same mileage. This weekend I did 300 miles at 50MPH and
got 28MPG (Canadaian)
2.4 liter automatic (4 speed) At 50MPH it feels like it is lugging. At
60 it runs freely and accelerates easily. In 2 weeks we will find out
what it does on a really long trip , at different speeds. Waterloo to
Montreal will likely be about 70mph to avoid being run over. From
there to Quebec City, ant then on to Riviere de Loup will likely be
60MPH, and across New Brunswick likely closer to 55. Cape Breton will
be 50-ish, and PEI likely closer to 45

 

[clare at snyder dot ontario dot canada]

in message


It is not a proven fact. You are thinking of thermal efficiency. You are
completely disregarding drag which is a very much more significant factor.
The thermal efficiency of a modern gas engine is between 25% and 30%. To
put that in layman's terms, every 100 gals you burn, only 25-30 is actually
converted to work. The rest is lost to heat. So, yes, it has its best
thermal efficiency at peak torque. However, the efficiency does not drop
significantly unless the engine is chugging at the lower end (incomplete
fuel burn) or pinging at the other end (predetonation). Everywhere else,
drag is the most important factor for the fuel economy of a car. At low
speed, most of the work the engine is doing is translated into movement of
the car. As speed increases, drag increases exponentially, and so does the
percentage of work used to overcome drag. At 40 MPH, about 10% of the work
the engine is doing is to overcome drag. By 55 MPH about 30% the work the
engine is doing is to overcome the drag. By 80 MPH, its more like 65%. by
100 MPH, it is like 90%.

An STi, at peak torque in 6th gear, is doing nearly 100 MPH. At that speed
gas mileage would seriously suck.

You did not read my message very well. I said the ENGINE - I'll quote
it:"The engine produces maximum hp/hr per lb of fuel at maximum torque
rpm. This is a well known proven fact".

I also said, earlier: "The optimum engine speed for fuel economy is
the maximum torque RPM."

Many vehicles are not geared properly to allow the engine to run at
this RPM without being heavilly loaded, or without the drag being too
high. It takes a very well designed car, aerodynamically, to allow
maximum VEHICLE fuel economy at maximum torque RPM. The gearing and
aerodynamics on the 1975 Celica GT just happened to be well enough
matched that the car DID get over 50MPG at 80MPH constant speed. (2AM
Sunday morning departure from Waterloo Ontario to Peterborough Ontario
- 2 adults in the car - 80MPH STEADY - did not put my foot down to
pass anybody, and never slowed below 75.
It is about 155 miles, and the one way trip took about 1/4 tank of
fuel. Return (round) trip took roughly 1/2 tank.

I am /was a VERY steady driver. NAVEX rallying demands it, and I
rallied competetively for 3 years - 4-3-2 finish in the province.
Economy runs require the same kind of discipline.
The trip to Peterborough was to "pit crew" for Taisto Heinonen and Tom
Burgess and the Team Toyota RA42 coupe in the fall of 1979 (I believe)
Tall Pines rally.

 

[Butch]

I have installed a trip computer on my 2001 Forester 2.5 AT.
See measured gas mileage driving highway with constant speed for at
least 15 miles:
MPH MPG
37 39
50 34
62 28
68 26
81 21

 

[JD]

I have installed a trip computer on my 2001 Forester 2.5 AT.
See measured gas mileage driving highway with constant speed for at
least 15 miles:
MPH MPG
37 39
50 34
62 28
68 26
81 21

That makes sense.

 

[JD]

in message

You did not read my message very well. I said the ENGINE - I'll quote
it:"The engine produces maximum hp/hr per lb of fuel at maximum torque
rpm. This is a well known proven fact".

Engine speed is nearly irrelevant for vehicle fuel economy in modern
engines. They are relatively efficient over a wide range of RPM.

I also said, earlier: "The optimum engine speed for fuel economy is
the maximum torque RPM."

Many vehicles are not geared properly to allow the engine to run at
this RPM without being heavilly loaded, or without the drag being too
high. It takes a very well designed car, aerodynamically, to allow
maximum VEHICLE fuel economy at maximum torque RPM. The gearing and
aerodynamics on the 1975 Celica GT just happened to be well enough
matched that the car DID get over 50MPG at 80MPH constant speed. (2AM
Sunday morning departure from Waterloo Ontario to Peterborough Ontario
- 2 adults in the car - 80MPH STEADY - did not put my foot down to
pass anybody, and never slowed below 75.
It is about 155 miles, and the one way trip took about 1/4 tank of
fuel. Return (round) trip took roughly 1/2 tank.

I can't believe that at all. The car would have to be nearly
aerodynamically perfect or only operating on two cyclinders to get that kind
of mileage at 80 MPH.

I am /was a VERY steady driver. NAVEX rallying demands it, and I
rallied competetively for 3 years - 4-3-2 finish in the province.
Economy runs require the same kind of discipline.
The trip to Peterborough was to "pit crew" for Taisto Heinonen and Tom
Burgess and the Team Toyota RA42 coupe in the fall of 1979 (I believe)
Tall Pines rally.

That may be true, but no matter how steady you are, you cannot overcome
physics.

 

[John O]

I also said, earlier: "The optimum engine speed for fuel economy is

I can't believe that at all. The car would have to be nearly
aerodynamically perfect or only operating on two cyclinders to get that
kind of mileage at 80 MPH.

80 can be 60 with a 20 tailwind. ;-)

-John O

 

[JD]

80 can be 60 with a 20 tailwind. ;-)

-John O

True

 

[Sheldon]

Yeah, I've been doing that since the beginning of the year up here too.
It's amazing how such a simple behaviour change results in such a huge
mileage improvement. We've been told about slowing down since the 1970's,
and it finally took $4+ gas to get us to obey it.

Up here in Canada there was a report that the local police forces are
definitely noticing everybody has slowed down, and fewer tickets are being
issued all across the nation.

Yousuf Khan

Not good. That means they'll lower the speed limits again because they're
not getting enough revenue from speeding tickets. :-(