Mods for better gas mileage

>
Newsgroups: rec.autos.makers.saturn
Sent: Tuesday, March 29, 2005 5:50 PM
Subject: Mods for better gas mileage

> That may be changing as well. I get significantly better mileage during
> long highway drives at 85 mph than at 65 - 70 mph (with all other factors
> being equal). I'm sure it depends a lot on the car - aerodynamics of the
> body, powerband of the motor, gearing, etc.

This is not believable if "all other factors" are truly equal. It would
take an incredibly poorly geared/designed vehicle with a badly tuned engine
to get better gas mileage at 85 than at 65. The aerodynamic drag increases
by 65% as you increase the speed from 65 to 85. If your car requires 20 hp
to go 65 mph, it will required at least 30 hp to go 85. Do you honestly
believe that your vehicle is so poorly designed that it is so much more
efficient with he engine running at 2000 rpm vs. 1500 rpm, that it can make
50% more power for less fuel? I think if you do a very careful comparison
where all other factors truly are equal, you will find that the vehicle gets
significantly better gas mileage at 65 than at 85.

Ed

In article <QeA2e.116609$r55.54447@attbi_s52>,
says...
> >
> Newsgroups: rec.autos.makers.saturn
> Sent: Tuesday, March 29, 2005 5:50 PM
> Subject: Mods for better gas mileage
>
> > That may be changing as well. I get significantly better mileage during
> > long highway drives at 85 mph than at 65 - 70 mph (with all other factors
> > being equal). I'm sure it depends a lot on the car - aerodynamics of the
> > body, powerband of the motor, gearing, etc.
>
> This is not believable if "all other factors" are truly equal. It would
> take an incredibly poorly geared/designed vehicle with a badly tuned engine
> to get better gas mileage at 85 than at 65. The aerodynamic drag increases
> by 65% as you increase the speed from 65 to 85. If your car requires 20 hp
> to go 65 mph, it will required at least 30 hp to go 85. Do you honestly
> believe that your vehicle is so poorly designed that it is so much more
> efficient with he engine running at 2000 rpm vs. 1500 rpm, that it can make
> 50% more power for less fuel? I think if you do a very careful comparison
> where all other factors truly are equal, you will find that the vehicle gets
> significantly better gas mileage at 65 than at 85.
>
> Ed

I believe volumetric efficiency has something to do with it. When an
engine reaches a certain RPM it can be running more effeciantly at 2000
rpm than at 1500rpm. IIRC the EPA's highway test speed is done at 47mph.
My cars EPA rating is at 28mpg highway however I still get that on a
cold day doing 75mph (2100rpm). It has nothing to do with bad designing
on part of the engine. It has to do with the engine reaching its best
range to flow air and get the most out of it while traversing more
terrain. Cars can often take advantage of higher speeds and gain mpg.
Larger vehicles usually cannot however.

----- Original Message -----
From: "blah blah" >
Newsgroups: rec.autos.makers.saturn
Sent: Wednesday, March 30, 2005 11:53 AM
Subject: Mods for better gas mileage

> I believe volumetric efficiency has something to do with it. When an
> engine reaches a certain RPM it can be running more effeciantly at 2000
> rpm than at 1500rpm. IIRC the EPA's highway test speed is done at 47mph.
> My cars EPA rating is at 28mpg highway however I still get that on a
> cold day doing 75mph (2100rpm). It has nothing to do with bad designing
> on part of the engine. It has to do with the engine reaching its best
> range to flow air and get the most out of it while traversing more
> terrain. Cars can often take advantage of higher speeds and gain mpg.
> Larger vehicles usually cannot however.

If you are talking about gas mileage differences at 35 and 45 mph, I can
believe you get better mileage at 45 than 35. However, once you get past 60
mph, aerodynamic drag is the major factor influencing fuel economy. For any
modern car or truck in a good state of tune, it is simply not believable
that the mileage is better at 85 than at 65 if all other factors are truly
equal. How are you even measuring your fuel economy at a steady 85? Or 65
for that matter. If you are doing 85, you have to be in an almost traffic
free environment, which is one factor that is probably not equal. I have had
this very discussion with a good friend over a beer. He makes the same
claim. Of course his high speed runs are across multiple sates on weekends
and late at night. His lower speed runs are in stop and go traffic on the
way to work, but never mind little things like that....

My 2003 Expedition (a huge box on wheels) has a rudimentary fuel computer.
It is hideously inaccurate. However, I have tried to check the indicated
mileage at various speeds from 55 to 75 (I won't drive 85). I have one
weekly trip of 140 miles on a lightly traveled road with various speed
limits, 55 /60 / 65 / 70.Several times for the different segments, I have
reset the fuel computer and checked it after ten miles of steady state
driving (mostly flat roads). The difference is always exactly as expected.
As the speed goes up, the fuel economy goes down. 75 (my personal max) is
about 3 mpg worse than 55 (15 versus 18). I know others with the same truck
who swear that thy get much better fuel economy at 80 that at 60. I say
hogwash. I believe it is poor data gathering, combined with a huge dose of
wishful thinking, sprinkled with just a little self delusion, and a lot of
grasping for an excuse to drive faster.

Ed

> I think if you do a very careful comparison
> where all other factors truly are equal, you will find that the vehicle
gets
> significantly better gas mileage at 65 than at 85.

Sorry, but I don't think that I will. I've owned the car for 12 years, and
put 130k+ miles on it to date. Gallons to fill, and miles traveled get
written down with every tank. And yes, that adds up to quite a bit of gas.
I pay particular attention to long trips. Over all those years, this
behavior has been consistently observed.

Doesn't matter much to me if you believe it personally, but I put it forth
here because that is what I have witnessed with my '94 SC2. No faith,
belief, or speculation. Observation based on 12 years of fact. I do not
attempt to generalize and apply this to any other cars. Each owner and
vehicle are different.

And as they say, "your mileage may vary". Quite fitting in this case.

Lane [ lane (at) evilplastic.com ]
---
Visit my Saturn Car Audio and Performance Page at http://www.evilplastic.com



"C. E. White" > wrote in message
news:QeA2e.116609$r55.54447@attbi_s52...
> >
> Newsgroups: rec.autos.makers.saturn
> Sent: Tuesday, March 29, 2005 5:50 PM
> Subject: Mods for better gas mileage
>
> > That may be changing as well. I get significantly better mileage during
> > long highway drives at 85 mph than at 65 - 70 mph (with all other
factors
> > being equal). I'm sure it depends a lot on the car - aerodynamics of
the
> > body, powerband of the motor, gearing, etc.
>
> This is not believable if "all other factors" are truly equal. It would
> take an incredibly poorly geared/designed vehicle with a badly tuned
engine
> to get better gas mileage at 85 than at 65. The aerodynamic drag increases
> by 65% as you increase the speed from 65 to 85. If your car requires 20 hp
> to go 65 mph, it will required at least 30 hp to go 85. Do you honestly
> believe that your vehicle is so poorly designed that it is so much more
> efficient with he engine running at 2000 rpm vs. 1500 rpm, that it can
make
> 50% more power for less fuel? I think if you do a very careful comparison
> where all other factors truly are equal, you will find that the vehicle
gets
> significantly better gas mileage at 65 than at 85.
>
> Ed
>
>

"Joe Blow" > wrote in message
...
snip
> - Overinflate the tire by a few PSI. Saturn recommends 26PSI, I use
> 32PSI.

I also use 32 psi and have nice even wear over face of tire tread and have
obtained over 140k km on stock Firestone tires.

> - Shift at the Saturn recommended speeds (ie. appx 2000RPM)

hoosier_drifter wrote Try early or "short" shifting when the
> oppurtunity presents itself (provided you have a manual.) Coast to stops
> whenever possible

the long version follows
IMHO

The Saturn S1 series single cam engine is tuned to produce its maximum
advertized torque at 2400 rpm. This max torque point is lower than most
similar vehicles and for me was the main reason I purchased these cars. The
max torque speed is usually the net speed for maximum volumetric efficiency.
Operation faster or slower will produce less HP/unitfuel. The Saturn S1
single cam will cruise at 110km/hr @ 2400 rpm.

The best fuel economy will be achieved by driving to minimize HP required.
Drag, (both aerodynamic and frictional) increases with the square of
velocity. Driving slower than optimal VE will reduce HP/unit fuel but will
require less HP due to reduced drag. Driving faster will reduce HP/unit
fuel AND will require MORE HP due to increased drag.

2400 rpm /65mph(110km/hr) is the sweet spot, and we want to accelerate up to
this speed in highest gear possible. Slightly slower will give greater
economy due to reduced drag.

The best way I know to limit both drag and HP required is to use the
technique the truckers call progressive shifting. In an automotive
application it requires that the vehicle be started in the lowest gear
available to minimize starting torque required and to maximize clutch life.
Use the minumum throttle required to obtain a smooth clutch engagement and
shift to second gear AS SOON AS the car is rolling.

For best distance/unitfuel always use the highest gear possible and minimize
the TIME spent in lower gears. Because of the torque multiplication, lower
gears do not require the full available torque to provide acceptable
acceleration and allow slower engine operation speeds. Shift through the
gears picking progressively higher shift points required due to the
increased drag at higher speeds. You want the resulting engine speed to be
UNDER 2400 rpm AFTER shifting to next higher gear. The exact shift points
will vary according to the load, the grade and the desired rate of
acceleration. If you are on a downgrade or are lighter you can use a lower
shift point, and higher loads and/or steep upgrade will require a shift
point above 2400 so that the AFTER shift rpm will be at or slightly above
2400 rpm max torque speed.

Gas engines are not built to survive long at high load/low speed operation,
in other words they do not like excesive lugging. The S1 series pulls quite
well above 1500 rpm or lower depending on load or grade. Minimizing engine
speed minimizes frictional drag and lowers piston speed resulting in lower
ring and cylinder wear provided that the temperature is kept up and the oil
changed as required. Short trips kill engines.

In my experience I seldom if ever need to exceed 3000 rpm and normally shift
around or well below 2000 rpm. It is important to be smooth and to take
advantage of rolling terrain to preserve your momentum. Ease off on the
throttle going up a hill and allow the vehicle to slow going over the top.
You will easilly regain your speed on the downgrade and will have a net fuel
saving.

ANY brake use wears the brakes and tires and wastes fuel Anticipating
required stops can allow a coasting stop or a rolling slowdown which is even
better. Watch how heavy truckers roll slowly rather than make a complete
stop at traffic lights.

> - Do not use more than 1/3 of the gas pedal travel.
>
> - Remove seats, carpeting, spare tire etc. to save weight.

Lighter is good but seats (removing rear seat lower cushion is easy and will
alow flat floor in SW) and carpet don't weigh much. Spare tire is a gamble.
VERY IMPORTANT remove unused roof racks and boxes when not required and keep
windows closed if possible.

YMMV
snip

-The Saturn S1 series single cam engine is tuned to produce its maximum
-advertized torque at 2400 rpm. This max torque point is lower than most
-similar vehicles and for me was the main reason I purchased these cars.
The
-max torque speed is usually the net speed for maximum volumetric
efficiency.
-Operation faster or slower will produce less HP/unitfuel. The Saturn S1
-single cam will cruise at 110km/hr @ 2400 rpm.

Interesting and ironic that two of my three Saturns are in fact SOHCs. And,
yes early shifting does benefit economy in these vehicles. Relying on low
end torque with minimal accelerator useage is something I learned to get me
by when driving a service truck on long distance trips, and not being near
enough to a service station that accepted my company's gas card. Sometimes
you have to stretch out that last bit of fuel to make it home. I don't
recommend doing this to any excess either in frequency or at extremely low
revs, but it does work.

"hoosier_drifter" > wrote in message
...
> -The Saturn S1 series single cam engine is tuned to produce its maximum
> -advertized torque at 2400 rpm. This max torque point is lower than most
> -similar vehicles and for me was the main reason I purchased these cars.
> The
> -max torque speed is usually the net speed for maximum volumetric
> efficiency.
> -Operation faster or slower will produce less HP/unitfuel. The Saturn S1
> -single cam will cruise at 110km/hr @ 2400 rpm.
>
> Interesting and ironic that two of my three Saturns are in fact SOHCs.
And,
> yes early shifting does benefit economy in these vehicles. Relying on low
> end torque with minimal accelerator useage is something I learned to get
me
> by when driving a service truck on long distance trips, and not being near
> enough to a service station that accepted my company's gas card.
Sometimes
> you have to stretch out that last bit of fuel to make it home. I don't
> recommend doing this to any excess either in frequency or at extremely low
> revs, but it does work.
>

I think we are agreed that low speed lugging is to be avoided, but that
above lugging, low end torque is where the SOHC engine really shines. I
have not experienced any of the oil consumption problems reported here and
always wonder if these problems are mainly found in DOHC engines (or SOHC
engines) driven in shall we say a more spirited manner. I think that low
speed operation also benefits timing chain and alternator and accessory belt
idler bearing wear, and that clutches and transmission syncros also last
longer when shifting at a lower than common speed.

I have found by experience and oil analysis that 6000 km seems to be a good
oil & filter change interval in our useage which is mainly highway. Oil
consumption seems to be more related to the quality of oil used and as I
normally use what ever is on sale have noticed some variability. Oil seems
to burn more as it ages in use so normally I just wait until the oil is down
to the add mark and then change it all. Our oldest car now has 235,000 km.
so is just getting to the age that our driving style will I hope be
returning the benifit of longer life before overhaul.

I have kept close track of every gas fill and have achieved a consistant 6.8
lt/100km (42m/imp gal) in mixed/city mainly mountain (3,5-4,500 ft
elevation) highway (Canadian winter) usage. My wife can get it down in the
high 5 low 6 range 50/mpg(imp)) on the highway but I have a heavier foot and
have never done that well.

Happy trails

My friend had an old GMC with a fuel economy gauge. I think it just worked
off vacuum. I installed an aftermarket vacuum gauge in my Mazda to help
detect some problem peculiar to the RX-7. Manifold vacuum, of course, drops
when the throttle is opened. If I watch the guage, my fuel mileage does
improve. For those who don't know, a 1.3 liter rotary can get from 10-30
mpg, depending on intake type and how you drive.

Chris