any ideas on better gas milage on my 95 yj
chris
4cy. so i was expecting to get ok milage with this. i just got a tune
up and i am switching tires from super swampers to all terains. im
putting on a new air filter. is there aything other things that would
help me out. i have heard mixed reviews on the tornado thing that goes
in your air filter that is supposed to give you more hp and better mpg.
any sugestions at all will be appreiciated.
thanks
chris
Mike Romain
to catch tail winds and to get lighter shoes....
Because of the power to weight ratio, the Jeep 4 banger gets about the
same mileage as the 6 gets. These engines are pretty tweaked stock.
Forget gimmicks and snake oil.
I have heard of some folks getting or doing a bored out throttle body to
use with headers but whether the power change is perception due to the
nicer sound or real is open to debate.
I would recommend you post over on rec.autos.makers.jeep+willys where
folks have these and try to tweak them.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
(More Off Road album links at bottom of the view page)
PeterD
What mileage are you getting? What kind of driving? How old/agressive
are you?
SnoMan
wrote:
>Because of the power to weight ratio, the Jeep 4 banger gets about the
>same mileage as the 6 gets. These engines are pretty tweaked stock.
Do you own one?? I'll bet not, I do in a 2000 Cherokee. Again you talk
about things you know nothing about.
The biggest problem a Wrangler has with the 2.5 AMC motor is drag
because it has the areo dynamics of a brick. Even with a 6 MPG can
suck at times. Tires play a big roll too. When you have bigger tires
you make effect drive ratio taller and the tires add more drag and MPG
will take a dump from them both combined. If MPG is your real goal
here, you want to keep tire size as stock as possible or regear Jeep
if they are bigger to keep engine in power range. Keep a fairly smooth
tread too as knobby tread consumes more power and cruise at 60 or less
to keep drag down. Running tires near max pressure will help also.
With my wifes Cherokee, she gets around 20 to low 20's in urban
driving to work with some city traffic. In winter it drops to high
teens on same route. On a trip up to get my daughters in college or to
vist them it gets about 23 to 25 MPG depending on how much you push
it. It has gotten as high as 27 since we bought it new on a long trip.
If you want to spend a bit of coin you could swap in a AX15 in place
of your AX5 because it has a taller OD (.78 vs .84) and it is a
sturdier tranny too (came with 6 cylinder) After 2000 Jeep started
using NV3550's with sixes and it has a slightly taller OD yet. To
swap tranny you need the bellhousing out of a 96 to 98 Dakota because
it used same engine as Jeep then when equipped with a 4 banger and the
same clutch slave setup to to make switch easier. This bellhousing
will make it possible to use a AX15, NV3550 or even a HD HV4500 (you
want the NV3550 over a NV3500 if you got that route because the 3550
was made as a bolt in replacement for AX15) 89 octane helps too as my
wifes Jeep picks up one or two MPG when using it and runs smoother
too.
-----------------
TheSnoMan.com
Mike Romain
banger?
LOL!
I won't even bother to address the rest of your fantasy.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
(More Off Road album links at bottom of the view page)
chris
i am getting about 12mpg right now. when i first got my jeep i was
doing a lot of offroading and i have superswampers on right now. i know
those tires are made for mud and are killing the mpg. i am 21 years old
now and i have tried to be less agressive on the road to try to keep my
jeep running as long as possible. i have also stoped offroading as much
i will only go maybe once every few months. i just bought a/t's so i
know the new tires will help. i just would like to get a little better
milage with the way gas is right now. people tell me to get a new car
but there is now way in hell i would ever sell my jeep lol
Mike Romain
That is extremely poor mileage. You should be up in the 20's on the
highway.
Even my old CJ7 with it's 258 and 33" tires gets a nice 23 mpg highway.
I have a t-case speedo gear change so the speedometer and odometer are
right on according to various GPS's and a 'measured "mile"'. (we have
km's up here instead of miles now, but my Jeep is in miles still)
What size are the tires? Oversized tires put the speedometer out so the
'perceived' gas mileage isn't the 'actual' gas mileage.
Oversized tires also blow the top gear's power band. Top gear is called
overdrive and with my 33's, it puts the engine rpm too low at 65 mph.
(1750 rpm) This causes the engine to lug when a slope or headwind hits,
which just drinks gas. If I use 5th, I lose at least 5 mpg or more. If
I forget about 5th and only use 4th for a top gear, it keeps the engine
in the rpm band it likes for mileage and power.
That would be worth a try.
Just a note. I found the mph difference at about 65 mph between 31's
and 33's to be about 6 or 7 mph with the same between 31's and the stock
29" tires. That means 33's could be about 15 mph off at 65 mph or close
to 24%.
SnoMan
wrote:
>You are trying to say in this post that a Dodge Dakota uses the 'AMC' 4
>banger?
Yes they did from 96 to 98 when equipped with a 4cyl but then you
would know that too "IF" you knew half of what you claim you do. You
do not have a prayer of a chance with outdoing me on Jeep hardware
because I have messed with them for almost 30 years now. (especailly
the ones that were still real Jeeps not this hybrids they make today
that are becoming more Dodge than Jeep with each passing year. (AMC
did far more to keep a Jeep a Jeep than Chysler ever did or will do.)
The Jeep briefly used the Pontiac 2.5 (also called GM Iron Duke) in CJ
from 80 to 83 but not after that and the AMC 2.5 with came out in 84
in Cherokee is based on a old AMC 232 with 2 cylinders lopped of and
yes again Dodge did use them for a few years in the dakota but not the
Jeep tranny as they used a NV3500 instead of a AX5 or AX15. This trick
with Dakota bellhousing is well known to hard core Jeep guys that
tinlker around and the reason you want those years and model is
because it also used the same slave cylinder setup as the Jeep so no
changes are need there in swap.
-----------------
TheSnoMan.com
SnoMan
wrote:
>That is extremely poor mileage. You should be up in the 20's on the
>highway.
Why do you tell him when you realy are kinda clueless? How many have
you owned???? CJ/Wranglers are never great MPG wise unless you drive
slow or with a tail wind and have smooth tires. Knobby tires can
realy hurt MPG on a 4 banger jeep, especailly oversized ones.
-----------------
TheSnoMan.com
Doug
of rpm's per mile. This is usually as slow as you can go and still be
in high gear. You get better mileage by flooring it and staying in high
gear up a hill than by downshifting. This is not intuitive, but needs
to be understood. A lot of us say, well gee, the car RUNS better at
higher rpm. That's true, but it gets worse gas milage. It feels like it
runs better because at higher rpms you have more torque and it
acclerates better.
Other than that, I dunno. It used to be you could lean your carburetor
and some other things, but you can't do any of that anymore as
everything is computer controlled fuel injection. You could get someone
to put an analyzer on your port and see if any error codes show up.
Also get a tailpipe inspection to make sure you aren't running rich for
some reason.
You guys keep changing your tire size and wonder why your gear ratios
are screwed up. Well, the gears are made for the tire size that comes
with the car, duh!!! Change the tire size and it's NOT going to be
ideal anymore. Have fun trying to re engineer your gear ratios to match
your new tire size. Its not a trivial task.
Jeep Wranglers don't get good mileage. My 4Runner is heavier than a
Jeep Wrangler and has more horsepower and gets better gas mileage than
a Wrangler. Not sure why that is, but I doubt you can tune the Wrangler
to match it. Maybe there is some chip change that can give you a little
more HP, I dunno.
Mike Romain
>
> On Thu, 23 Nov 2006 10:52:57 -0500, Mike Romain <rom...@sympatico.ca>
> wrote:
>
> >You are trying to say in this post that a Dodge Dakota uses the 'AMC' 4
> >banger?
>
> Yes they did from 96 to 98 when equipped with a 4cyl but then you
> would know that too "IF" you knew half of what you claim you do. You
> do not have a prayer of a chance with outdoing me on Jeep hardware
> because I have messed with them for almost 30 years now.
You seem to think this is some kind of competition?
(especailly
> the ones that were still real Jeeps
I know this senile old bugger on another group that thinks the same.
You two would likely get along fine.
not this hybrids they make today
> that are becoming more Dodge than Jeep with each passing year. (AMC
> did far more to keep a Jeep a Jeep than Chysler ever did or will do.)
> The Jeep briefly used the Pontiac 2.5 (also called GM Iron Duke) in CJ
> from 80 to 83 but not after that and the AMC 2.5 with came out in 84
> in Cherokee is based on a old AMC 232 with 2 cylinders lopped of and
> yes again Dodge did use them for a few years in the dakota but not the
> Jeep tranny as they used a NV3500 instead of a AX5 or AX15. This trick
> with Dakota bellhousing is well known to hard core Jeep guys that
> tinlker around and the reason you want those years and model is
> because it also used the same slave cylinder setup as the Jeep so no
> changes are need there in swap.
I don't follow Dodges much or 4 bangers for that matter and that hack
job on the bell housing is well.... interesting to say the least. 'I'
sure wouldn't want my tranny's input shaft hanging in mid air only held
by an 1/8" thick tube of soft porous bronze. I like mine in the center
of the crank or maybe flywheel so it is held solid in place. I also
wouldn't want my slave propped up with shims to 'maybe' work or to maybe
drag and kill throwouts or front seals. To each their own I guess.
LOL!
Jon R. Pickens
> You will get the best gas mileage possible by running the least number
> of rpm's per mile. This is usually as slow as you can go and still be
> in high gear. You get better mileage by flooring it and staying in high
> gear up a hill than by downshifting. This is not intuitive, but needs
> to be understood. A lot of us say, well gee, the car RUNS better at
> higher rpm. That's true, but it gets worse gas milage. It feels like it
> runs better because at higher rpms you have more torque and it
> acclerates better.
Not remotely true. Flooring it will kick the engine into "power mode"
where the fuel/air mix gets richer to try and produce more power to
keep up with the increased engine load. I don't know what fuel/air
ratio his computer-controlled engine makes when in power mode, but it's
going to be more fuel for sure. This is a simple concept that's been
around since the carburetor days. My Edelbrock carb on my Blazer goes
into power mode when the manifold vacuum drops to around 6" Hg. BTW, I
don't have to floor it to get the vacuum that low.
Lugging along in too high of a gear can be as bad or worse for fuel
economy. The best gas mileage will be achieved when the engine is
spinning at the RPM where peak output (torque) occurs. Peak torque (by
no coincidence) occurs when the engine is at peak efficiency. My
everyday car has a 5-speed manual, and once I trained myself to stop
driving in the highest gear possible, my MPG has gone up considerably.
Where my weekly commute to and from work (30 miles each way, 300 miles
total every week) used to average around 23mpg (according to the
onboard computer) I now get around 27.5mpg, and have at time gotten up
to 29-30mpg when traffic was lighter. Not bad when considering that
1/3 of that driving is on back roads and/or streets with several stop
signs and red lights, and many hill-climbs.
> Other than that, I dunno. It used to be you could lean your carburetor
> and some other things, but you can't do any of that anymore as
> everything is computer controlled fuel injection. You could get someone
> to put an analyzer on your port and see if any error codes show up.
> Also get a tailpipe inspection to make sure you aren't running rich for
> some reason.
I don't know which computer his Jeep has, be it OBD-I or OBD-II. If
it's the latter (not likely), he can install a Scangauge II
(http://www.scangauge.com/) and watch the MPG in real-time as well as
your average over a period of time. I can't view real-time MPG in my
car, but I want one of these for that exact reason.
Watching my vacuum/boost gauge helps me adjust my driving technique for
better mileage. My car is turbo-charged, and when the boost rises,
fuel has to rise as well to keep the ideal fuel/air ratio in check.
More boost = more gas. By keeping it as low as possible my MPG has
gone up considerably. I only lay into the pedal when getting on the
interstate now or when trying to quickly get around another driver
who's likely to cause a wreck.
Even without a turbo, a vacuum gauge can provide a visual aid to keep
gas consumption at a minimum. When you gun it, manifold vacuum will
drop to almost zero (atmospheric pressure). Between that and the tach,
I have pretty much figured out how to keep the engine in its ideal
operating range for economy.
> You guys keep changing your tire size and wonder why your gear ratios
> are screwed up. Well, the gears are made for the tire size that comes
> with the car, duh!!! Change the tire size and it's NOT going to be
> ideal anymore. Have fun trying to re engineer your gear ratios to match
> your new tire size. Its not a trivial task.
The OP never mentioned anywhere that his tire size (diameter) changed.
However, the tread of the mud tires will have quite a bit more "rolling
resistance" as compared to the street tires, which does hurt MPG.
If he did change to bigger tires, getting the right gear ratio figured
out is fairly simple.
Go here: http://www.ring-pinion.com/content/calculators/RPM.asp
Plug in the axle ratio along with the original tire size... make a note
of the RPMs at a given speed. Plug in the new tire size and then play
with different axle ratios to get the engine RPMs back where they need
to be at the same speed.
> Jeep Wranglers don't get good mileage. My 4Runner is heavier than a
> Jeep Wrangler and has more horsepower and gets better gas mileage than
> a Wrangler. Not sure why that is, but I doubt you can tune the Wrangler
> to match it. Maybe there is some chip change that can give you a little
> more HP, I dunno.
Well "Duh"... (to quote you). If your motor is producing more power at
the speed that you drive it's likely because it's at an ideal RPM (and
therefore making closer to peak torque) when you're cruising along.
Horsepower is a derived value that describes work done over a period of
time (work being torque, time being RPM). Peak HP almost always occurs
at a much higher RPM than peak torque. My current engine is in no way
optimized for the truck it's installed in. Peak HP occurs at around
5200rpm--an engine speed that I *never* bothered to achieve (and don't
plan to). Adding a "chip" to increase HP won't do much for his torque
needs. At least not enough to put a dent in his terrible gas mileage.
Max MPG will only be achieved when the engine is running at peak
efficiency (the ideal RPM) with *any* given tire size or gearing
combination. Before my engine swap, my K5 Blazer got 17mpg on the
highway with 31" A/T tires and the stock 305ci motor (with over 100k on
it) and 3.08 axle gears. I can't imagine that a smaller and lighter
Jeep couldn't achieve the same. That's not great mileage, but it's
certainly better than what he's experiencing now.
MPG goes out the window when you're driving a vehicle that's pretty
much built for off-road use. On the other hand, a street-only vehicle
can be optimized for max MPG while sacrificing off-road performance.
The key here to find a good balance that he can live with.
~jp
Doug
readout and take a look at the gas mileage you are getting at different
speeds. You almost always get best gas mileage at 30mph or so (which is
approximately 1250 rpm).
Jon R. Pickens
> If you don't believe me sit in a car with a real time LED gas mileage
> readout and take a look at the gas mileage you are getting at different
> speeds.
Which car is this and does it have a real-time MPG gauge? I've only
seen one car that had a real-time gauge from the factory. Otherwise
most cars that report MPG are only showing an average MPG.
If you're coasting, meaning the engine is using little to no effort to
move the car along, then yes... I can drop to neutral in any car, and
while coasting the "real time" MPG is pretty high--until it slows down
to the point where I actually need the engine to keep me moving.
If I reset my average MPG gauge then for the first mile or so it's
pretty much "real time". Your theory of "flooring it" in a high gear
to achieve higher MPG is just plain wrong.
> You almost always get best gas mileage at 30mph or so (which is
> approximately 1250 rpm).
If geared to achieve 30mph at that RPM, most vehicles would have almost
no ability to pull itself back up to a higher speed or even maintain
that speed up a hill...In a diesel maybe...
I can get down to 1250rpm at 30mph, no problem--I just won't be able to
maintain it for very long. You're assuming that all engines are the
most efficient at 1250rpm. That's wrong. Ever heard of volumetric
efficiency? Do you understand how VE affects power and economy?
I've observed exactly the opposite phenomenon in my own car as well as
others. In mine, the vacuum gauge drops to zero then goes into boost,
which means *more* gas is being used. Even without the turbocharger,
this would be true. Not as much gas would be used as in a
turbo-charged car, but it would still be more than maintaining a much
lighter load (meaning lower gear) at a reasonable (higher) RPM.
You're going to have to do better... Try providing some actual
knowledge about how fuel systems and gearing affect MPG.
~jp
Doug
http://content.hamptonroads.com/story.cfm?story=101517&ran=44674
Car manufacturers are making transmissions with overdrive ratios quite
dramatic, so it may have gone up from 30 to 40 since rpm at cruise is
lower than without "overdrive".
A Ford Explorer Eddie Bauer I was in had a real time mpg readout.
Slower we went, better the mileage. No suprise. This was WELL
established in a series of tests in Detroit in the 1930's. Things have
changed a little, but not all that much. Fuel injection and so forth
yes. Turbo charging does change things a bit. My comment about flooring
it to make the hill as opposed to downshifting was for normally
aspirated. Turbos do change the equation.
Doug
You MAY have to drive a little faster if you have a high gear
overdrive. Very little throttle required. No you don't have much
acceleration from this configuration, but you DO get good gas mileage.
Go out and try it. I have a manual, so of course its no problem at all.
Some automatics might need the higher speed to stay in high gear. Again
this is on LEVEL ground.
SnoMan
wrote:
>SnoMan wrote:
>>
>> On Thu, 23 Nov 2006 10:52:57 -0500, Mike Romain <rom...@sympatico.ca>
>> wrote:
>>
>> >You are trying to say in this post that a Dodge Dakota uses the 'AMC' 4
>> >banger?
>>
>> Yes they did from 96 to 98 when equipped with a 4cyl but then you
>> would know that too "IF" you knew half of what you claim you do. You
>> do not have a prayer of a chance with outdoing me on Jeep hardware
>> because I have messed with them for almost 30 years now.
>
>You seem to think this is some kind of competition?
No just distain for comments from those that realy do not know the
subject well
>
>(especailly
>> the ones that were still real Jeeps
>
>I know this senile old bugger on another group that thinks the same.
>You two would likely get along fine.
Doubtfull.
>
> not this hybrids they make today
>> that are becoming more Dodge than Jeep with each passing year. (AMC
>> did far more to keep a Jeep a Jeep than Chysler ever did or will do.)
>> The Jeep briefly used the Pontiac 2.5 (also called GM Iron Duke) in CJ
>> from 80 to 83 but not after that and the AMC 2.5 with came out in 84
>> in Cherokee is based on a old AMC 232 with 2 cylinders lopped of and
>> yes again Dodge did use them for a few years in the dakota but not the
>> Jeep tranny as they used a NV3500 instead of a AX5 or AX15. This trick
>> with Dakota bellhousing is well known to hard core Jeep guys that
>> tinlker around and the reason you want those years and model is
>> because it also used the same slave cylinder setup as the Jeep so no
>> changes are need there in swap.
>
>I don't follow Dodges much or 4 bangers for that matter and that hack
>job on the bell housing is well.... interesting to say the least. 'I'
>sure wouldn't want my tranny's input shaft hanging in mid air only held
>by an 1/8" thick tube of soft porous bronze. I like mine in the center
>of the crank or maybe flywheel so it is held solid in place. I also
>wouldn't want my slave propped up with shims to 'maybe' work or to maybe
>drag and kill throwouts or front seals. To each their own I guess.
>LOL!
I am not a Dodge fan but I do try to keep track of what parts Dodge
has swapped around. Usually it is Dodge parts in a Jeep rather than
Jeep part is a Dodge. Pretty soon a they are going to have top change
the name of a Jeep to something else because not much of it left in
some models other than name
>
>Mike
>86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
>88 Cherokee 235 BFG AT's
>Canadian Off Road Trips Photos: Non members can still view!
>Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
>(More Off Road album links at bottom of the view page)
-----------------
TheSnoMan.com
Jon R. Pickens
article that, while being truthful about wind resistence, in no way
addresses the fact that fuel consumption increases with load at *any*
given RPM. The fact that you found an article with little scientific
info doesn't do much to back your claims.
The point of the whole thread is to assist the OP with getting better
mileage with his existing vehicle under *his* driving conditions. My
comments all deal with getting the engine in its peak efficiency range.
Yours do not.
When an engine is operating at peak efficiency that means it's doing
the most work for every drop of fuel consumed. Period.
Again, if you're coasting along and barely touching the gas then for
short sprints the MPG will probably be pretty good. But those gains
will quickly be negated when you need to accelerate or maintain speed
up even the slightest grade. Why? Because most engines aren't capable
of producing peak torque at 1250rpm.
Even with a naturally aspirated engine, fuel consumption will increase
with load. As the load increases (more speed, heavy acceleration,
going up a hill, etc...) you'll give it more gas, which causes manifold
vacuum to drop, which, in a carb, physically makes changes to richen up
the mix for more power. A computer controlled engine will do the same
thing.
A heavier load on the engine at a given speed in a given gear will
equal more fuel comsumed... Period.
At 30mph, and around 1250rpm, I'd be in 4th gear. To accelerate or
maintain speed up a hill, I must give it quite a bit of gas. You can
hear the engine bog down, sometimes accompanied by a shimmy as the
engine struggles to keep up. Some vehicles will emit black smoke from
the tailpipe from the richer fuel/air mixture. Even with my
turbo-charged engine in a car with a good power/weight ratio this is
true.
~jp
Jon R. Pickens
and neither does the gas pump.
~jp
Doug
driving at 30mph, just that most cars will get better gas mileage as
you slow down and to stay in as high a gear as possible.
You seem stuck on "most efficient at maximum torque". If you define
"most efficient" as the CAR getting the best gas mileage, this is not
true. For best gas mileage, you need to consider the entire drive
train.
How do YOU define "most efficient"? If your definition is the ENGINE
producing the most power for the least amount of gasoline that is one
thing. If "most efficient" is the car going the most number of miles on
a gallon of gasoline, that is another thing.
As for the going up the hill thing. My point is, if your choice is to
make it up the hill with the throttle floored in highest gear or
downshifting, you WILL get the best gas mileage by staying in high
gear.
These two items are necessary to understand and believe before you can
understand how to get best gas mileage in a car. Then use these
techniques when you drive to maximize your gas mileage.
You don't like my link, buy you do not present ANY link whatsoever of
your own in rebuttal. You just say mine isn't any good. And if given
overwhelming evidence of me being correct, I doubt you would post ANY
rebuttal of substance as you don't seem to want to consider that you
might not be seeing the entire picture. Perhaps you CAN learn, I don't
know. Then again, maybe not. Maybe you think you know everything and
can't learn any more. As for me, I am willing to learn. If I am wrong,
I will change. But I don't think I am wrong here.
The least number of RPM's per mile will give best gas mileage. That is
my underlying principal that I don't think is wrong.
The other things are techniques to achieve good mileage based on that
principal. This stuff isn't rocket science. Any automotive engineer
knows this. But it isn't taught much, so people dont learn it. Instead
they drive, notice the car is more responsive at higher rpm, and figure
it must run "more efficiently" at those higher rpms. The car does "run
better" in that it accelerates better. But IT USES MORE GASOLINE doing
it. Which if you think about it makes sense. A peppier car will use
more energy going somewhere. Drive slow and steady, you will be less
peppy, but will use less gasoline....
And for this argument, I am going to have to leave turbo out of the
equation, It may change things. Unless someone wants to give some
evidence on what the principals of driving would be different if you
have a turbo. I just don't know. They may not differ, then again they
might.
Jon R. Pickens
> You have some valid points about practical driving. I wasn't advocating
> driving at 30mph, just that most cars will get better gas mileage as
> you slow down and to stay in as high a gear as possible.
If gas were consumed on a linear scale, meaning that the fuel/air ratio
was 100% constant throughout both the entire RPM range and also under
all driving conditions, then yes, the slowest engine speed possible
would consume the least amount of fuel. But your argument does not
address those other points as I have.
> You seem stuck on "most efficient at maximum torque". If you define
> "most efficient" as the CAR getting the best gas mileage, this is not
> true. For best gas mileage, you need to consider the entire drive
> train.
I never said that the entire drivetrain wasn't part of the equation...
don't you remember earlier in the thread where I advocated getting his
gearing to match up with his engine's peak output? Gears that are too
low would spin the engine much faster than it would need to in order to
effectively drive the vehicle forward, which can of course, hurt fuel
economy. Gears that are too high put an unnecessary load on the engine
which can also hurt fuel economy.
If the engine makes peak torque at 2000rpm, then your best gas mileage
in 1st gear would be at 2000rpm. As soon as you shift to 2nd, engine
RPM drops, load increases, fuel economy drops a bit until you get the
engine up to it's peak output range again.
In that case, running 2000rpm in 5th gear, with little load on the
engine would move the vehicles the longest distance per drop of fuel.
> How do YOU define "most efficient"? If your definition is the ENGINE
> producing the most power for the least amount of gasoline that is one
> thing. If "most efficient" is the car going the most number of miles on
> a gallon of gasoline, that is another thing.
Depends on what we're talking about. The engine has an ideal operating
range (rpm) at which it'll be most efficient in terms of both fuel
comsumption and power output.
In terms of distance per drop of fuel, it's a function of keeping the
engine at it's ideal operating range through gearing and driving
technique.
Simply put, when the engine is at it's peak output (making the most
power per drop of fuel) then you will get the most mileage in any
particular gear. More miles in 5th gear than 3rd obviously... But
still, you'll go further in the same gear if the engine is at its most
efficient. Gas consumption is *not* a linear scale that's directly
linked to RPM. The amount of load placed on the engine will affect the
fuel/air ratio. That's how all fuel systems on cars work, be they
carbed or fuel-injected, naturally aspirated or forced induction.
> As for the going up the hill thing. My point is, if your choice is to
> make it up the hill with the throttle floored in highest gear or
> downshifting, you WILL get the best gas mileage by staying in high
> gear.
No... the fuel/air mix will be richer because you floored it, meaning
more gas comsumed to go the same distance. In many cases, more gas
will be consumed than if you'd down-shifted and spun the engine at a
higher RPM.
I used to try to stay in the highest gear possible at all times. I
stopped doing that. My fuel economy has increased. The onboard
computer doesn't lie, the gas pump doesn't lie, and my bank statements
don't lie. I have increased my mileage in terrible rush-hour driving
conditions from 23mpg (average for the week) to 28, sometimes 29+mpg.
I did this by paying attention to the load placed on the engine. A
vacuum/boost gauge is a good indicator of how hard you're pushing the
engine. I watch that gauge like a hawk now when I'm in
bumper-to-bumper traffic. It makes a difference. More vacuum means
I'm keeping my foot out of the gas pedal, and that equates to better
fuel economy.
> These two items are necessary to understand and believe before you can
> understand how to get best gas mileage in a car. Then use these
> techniques when you drive to maximize your gas mileage.
The fact that you directly link fuel consumption to engine RPM shows
your lack of understanding on the subject.
> You don't like my link, buy you do not present ANY link whatsoever of
> your own in rebuttal. You just say mine isn't any good. And if given
> overwhelming evidence of me being correct, I doubt you would post ANY
> rebuttal of substance as you don't seem to want to consider that you
> might not be seeing the entire picture. Perhaps you CAN learn, I don't
> know. Then again, maybe not. Maybe you think you know everything and
> can't learn any more. As for me, I am willing to learn. If I am wrong,
> I will change. But I don't think I am wrong here.
I didn't present a link because I don't consider it to be factual info
just because I pulled it off some website. I don't need to present a
link to defeat your argument. That link you sent has truth in there
about the effect wind resistance plays in fuel economy. But it's only
part of the equation.
I'm not saying it's not "good", just that it's not complete. It
doesn't tell the whole story, which is what I'm trying to do here. You
seem to have a problem with that.
Which makes it funny that you state that *I* am not seeing the whole
picture. I keep filling in the other pieces of the picture while you
keep focusing on engine RPM only. You don't consider load or any of
the things that will affect the engine's load such as vehicle weight,
aerodynamics and wind resistance, increased rolling resistance from the
OP's use of mud tires over street tires, driving on any surface other
than a level grade, etc...
> The least number of RPM's per mile will give best gas mileage. That is
> my underlying principal that I don't think is wrong.
All engines have an optimal operating range for power and efficiency.
If engine efficiency was constant, and fuel consumption were tied
directly to engine RPM as you believe, then under equal driving
conditions spinning the engine at a lower RPM would indeed result in
lower gas consumption as you state. Unfortunately, that's not the
case. Lugging along in 4th gear below 1300rpm at 30mph in my car, or
just about any car, will put a much heavier load on the engine than
running in 3rd gear at a higher RPM. That's just the plain truth of
it.
You are refusing to address the fundamental principles on which an
engine operates, while ignoring real-world driving conditions. The
earth is not flat!
> The other things are techniques to achieve good mileage based on that
> principal. This stuff isn't rocket science.
Really... because you seem to have an awful hard time understanding it.
> Any automotive engineer knows this. But it isn't taught much, so
> people dont learn it.
Ah yes... Those damn automotive engineers and their conspiracies...
trying to make the rest of us spend more on gas!
> Instead they drive, notice the car is more responsive at higher rpm,
> and figure it must run "more efficiently" at those higher rpms. The car
> does "run better" in that it accelerates better. But IT USES MORE
> GASOLINE doing it.
So an engine produces more power as it turns faster? Interesting. Do
you wonder then why both torque and HP will begin to drop after a
certain point? It's because the engine is past its most efficient
operating range.
Ever wonder why we even need accelerators? If we didn't need to
increase the engine speed then we could all just drive around with our
cars idling.
> Which if you think about it makes sense. A peppier car will use
> more energy going somewhere.
That depends on many factors. My 4cyl turbo-charged car uses a whole
lot less gas and moves a whole lot faster than my Blazer with a 350.
The 350 burns a lot more fuel (energy), yet...I'm going slower...
Hmm...
> Drive slow and steady, you will be less peppy, but will use less gasoline....
That's a given...but I never mentioned anywhere that gunning it was the
way to better gas mileage. You on the other hand, did...
> And for this argument, I am going to have to leave turbo out of the
> equation, It may change things. Unless someone wants to give some
> evidence on what the principals of driving would be different if you
> have a turbo. I just don't know. They may not differ, then again they
> might.
Why leave that out? The fundamentals do not change whatsoever. At any
given RPM more fuel is needed to generate more power. Forced induction
just means you can push more fuel and air into the engine thus
increasing its volumetric efficiency. It still burns fuel and air.
I've already told you the principles of driving with forced induction.
Where most engines reach atmospheric manifold pressure when the gas
pedal is on the floor, a turbo-charged engine will increase the
pressure above atmospheric, which is measured in pounds of boost. If
air, and only air were being added, the engine would just starve for
fuel by being run too lean. The carb or fuel-injection setup adds fuel
accordingly and the car makes more power...pretty simple.
Why don't you revisit that thread you participated in regarding diesel
engines...
Here's a link for you...
http://groups.google.com/group/rec.autos.4x4/browse_frm/thread/46e8d74bbc2830f0/#
Read your messages and the responses by Willem-Jan Markerink and
myself. Think about it.
I'm starting to think you're a troll...
~jp
Doug
You want specific and scientific, there it is.
A mile is a distance. A gallon is a certain volume of fuel.
EFF = miles/gallon
What is your definition of efficient?
Jon R. Pickens
fuel efficiency of a vehicle.
The whole point of the thread is to increase MPG...or the overall fuel
efficiency of a vehicle. To do that you must understand the efficiency
of the engine, which, at this point I'm giving up trying to explain to
you. You obviously don't get it and aren't going to anytime soon.
You continue to avoid discussion of the inner workings of an engine or
even part of one (the fuel system) which indicates a lack of knowledge
on the subject. And your link dealing with how wind resistance affects
gas mileage did more to reinforce my argument (wind resistance =
increased load) than it did to support yours. We haven't even
scratched the surface of drivetrain losses and how gearing affects
power actually delivered to the wheels.
The fact that you're not addressing, rebutting, or even acknowledging
the points raised in my previous posts further leads me to believe that
you don't know what you're talking about and are indeed just a troll
trying to stir something up.
FYI, efficiency is not usually "defined as a ratio"...which would make
no sense. Efficiency is "expressed" as a percentage. For example, if
a given engine converts 30% of the heat content of the fuel (expressed
in BTUs) to usable force, that would make it 30% efficient. The same
engine with a good fuel system may extract 95% of the heat content from
the fuel. That means it's 95% efficient in terms of converting fuel to
torque, and only 5% of the fuel is wasted. But still, only 30% of the
fuel's energy comes out the crankshaft.
A ratio such as Miles per Gallon can be used as a handy way of gauging
the fuel consumption of one car over another, but it's hardly an
accurate means of describing true efficiency.
~jp