How can i get more fuel economy? I'm at my wits' end!

[BBowers]

I appreciate the 23 degree aero approach. I was hoping someone would write in and say, ditch that Bullydog, get a " " I got an extra blank miles per gallon from using this box/tuner. Or, try this turbo, I don't know, throw me a bone here!

 

[cerberusiam]

I appreciate the 23 degree aero approach. I was hoping someone would write in and say, ditch that Bullydog, get a " " I got an extra blank miles per gallon from using this box/tuner. Or, try this turbo, I don't know, throw me a bone here!

There is no "bone", no "silver bullet" for better mpg. :-laf It is what it is.



Every truck reacts differently to every combination. The ONLY thing you an do is try different things and see what happens.



You could do one of these:



1. Move to the desert at elevation 3-4k feet. Dryer thinner air, warm temps, and flat roads equal better mpg. Sea level and cools temps kill the mileage.



2. Reprogram the ECU for a single injection event, replace the cam with one designed for single injection, remove all the emissions items, reset all the axles gear setups and use synthetics all thru the truck.



3. Buy an 03.





How much do you want to spend to get a couple miles per gallon? What do you want to give up for a nominal increase? It's all about "choices".

 

[DPKetchum]

First thing that hit me when I read the post was the tires/size. Everyone I've ever known with BIG tires got poor mileage and anyone I've ever known to buy a 4x4 with BIG tires couldn't wait to get them off the truck. Maybe its the guys I know but thats been my experience for years. Friend of mine just bought a clean one owner 95 12valve(paid 7k) with 100k on it with BIG tires and hates them. Fixing to chunk them for the correct size truck came with.

 

[fkovalski]

... . Sea level and cools temps kill the mileage... .

Help me out on this ... . I am under the impression that seal level is better for milage (more air to combust) as opposed to less at altitude (heck, I breathe better at lower altitude) and cooler temps allow for more dense air to mix with fuel, hence more power (or better milage if light- footed)

 

[Rattlin_Ram]

You have a truck with 35" tires that gets 17+mpg and you are complaining????



Put smaller, narrower, harder tires on it, and I'd be willing to bet you'd pick up a couple mpg... or be like me and just live with the mileage because you like the look of the tires...

 

[jelag]

I have skimmed some of these posts... . I'd like to add a couple of comments to this thread.....

If there was a way to get say 10% better fuel economy with these trucks at a reasonable expense DC would be doing it... . They are under C. A. F. E. which is an EPA mandate... . Corporate Average Fuel Economy CAFE is the average of the fuel economy of the vehicles sold each year... if they fall into the guidelines they get a pat on the back by the EPA and if they fall out they get nice big fines... . In some cases they almost give away a car that gets 30 mpg to keep the fleet rate up so that they don't get fined...

With CAFE in mind, they would spend 1000 per truck to get that 10% if they could... . so most of the stuff that's talked about to increase fuel economy is what I call snake oil...

As an engineer I learned that to move a mass, with a certain amount of wind resistance to speed and later down the road requires a certain amount of HP. . this can be computed on a chassis dyno and I've personally spent at least 1000 hours in my life working with one of these on many vehicles...

What I've personally learned is that the best way to get better fuel economy is to let my wife drive..... she does all the right things... and frankly on the same run with the same vehicle gets better economy...

I could write pages on the things I've actually tested on the chassis dyno and found none of them worth their weight in fuel economy...

Just my 2 cents worth...

 

[GOT-Torque]

Jim, you beat me to it! LOL



Just let your wife and/or girlfriend drive. Be careful, only one of them at a time Works for me everytime. I pick up atleast 2 mpg with that alone.



The day I drove the truck home, bone stock (190 hp to the ground or so), I got 20. 5 mpg.



Today (with nearly 3 times the hp) I get anywhere between 15 and 18 depending on many things. But you can't get the grin of my face when I'm driving it.



No complaints here.

 

[AKaiser]

Brother, you're pushing 7000lbs of steel thru the wind. As sea level air is more dense than at, say 5180 feet, you're going to have more wind resistance at sea level. Part of the reason the 94-02 trucks got better fuel economy is they pushed less wind. In order to make the newer trucks safer in a front impact, they had to make it a bit taller, thus spreading the front impact over a larger area and volume. My 99 half-ton gasser couldn't touch this thing, fuel economy-wise, though. I get an average 2-3 MPG better with the much heavier diesel truck. As for the tire size, there's a sweet spot. I went from 265/70R17s to 275/70R18s and gained 0. 5 MPG. It depends on your gear ratio, transmission, and tire size combination, and of course, engine dynamics. The faster you move thru the air, the loss in MPG increases logarythmically. It's not a 1:1 thing. Mine does 18-19 at 60, 16. 5 at 75, and 11. 5 at 85.

 

[cerberusiam]

Help me out on this ... . I am under the impression that seal level is better for milage (more air to combust) as opposed to less at altitude (heck, I breathe better at lower altitude) (or better milage if light- footed)

Lower altitudes generally equal denser air, which is harder to move an object thru. This translates a power cost that shows as mileage decrease. Cool air acts the same way at higher altitudes. It is denser and even though the barometric pressure is less, it still requires more power to to move thru it.

and cooler temps allow for more dense air to mix with fuel, hence more power

This works well with a normally aspirated gas engine and has exactly the opposite effect on a diesel. Adding cooler denser air to a combustion event will REDUCE power not increase it. The same will happen if if the humidity is high and there are too many water grains in the air. A diesel combustion event relies on a stoichiometeric balance to create the optimal power. Change the mixture and power drops. In the case of more dense air, the fuel burns out before it can reach the higher temps to create maximum power. In addition the denser air takes more to heat thereby reducing the amount of energy available to convert to power.



The IC and turbo on these trucks is pretty efficient at creating a charge that is pretty optimal for power generation. My truck will consistently make 22-23 mpg at 65 mph running at 3k feet in 100+ degree temps, even with the AC blasting. As soon as the temps and/or elevation start droppings so does the mileage. Best consistent mpg I see is high desert in the summer.

 

[cerberusiam]

As an engineer I learned that to move a mass, with a certain amount of wind resistance to speed and later down the road requires a certain amount of HP. .

. . and to create HP fuel needs to be burned. It's a zero sum game. IF you want to drive 75 mph, at sea level, in a high profile 7000 lb vihicle with 325 available HP; don't expect 25 mpg on a regular basis. The laws of physics just don't bend to our will no matter how much we wish it. :-laf :-laf

 

[fkovalski]

cerberusiam,

I can sort of follow your explanation... . but can you expand further and elaborate on why I have exessive smoke at my altitude (9,000+ feet) and less at Denver when (if I understand from your reply) that "... at higher altitudes It is denser... ". I kinda' thought that at altitude my truck is sorta' running "richer" due to less air available- hence more smoke. My milage is better at lower altitudes... . and (if I read your reply correctly) one should get better milage at higher altitude?



Thanks,

-frank.

 

[cerberusiam]

cerberusiam,

I can sort of follow your explanation... . but can you expand further and elaborate on why I have exessive smoke at my altitude (9,000+ feet) and less at Denver when (if I understand from your reply) that "... at higher altitudes It is denser... ". I kinda' thought that at altitude my truck is sorta' running "richer" due to less air available- hence more smoke. My milage is better at lower altitudes... . and (if I read your reply correctly) one should get better milage at higher altitude?



Thanks,

-frank.

You need to move lower!! Can anything LIVE at 9000+ feet?? :-laf :-laf

Cool air acts the same way at higher altitudes. It is denser and even though the barometric pressure is less, it still requires more power to to move thru it.

You have to take the whole statement in context and respect the period. At higher altitudes cool air is denser than warm air and it effects things the same as a lower altitude.



At 9000+ feet you are out of the "zone of influence" and into a point blank lack of air. Much over 6000 ft and the ability of the turbo to make enough good air is going down hill quickly. I'll bet your boost is considerably lower up there to, huh?

 

[231jasonS]

UMMM, Derek do you have a lot of time on your hands?

 

[rbattelle]

I hope you don't drive like a granny all the time Too much easy driving and it will lose MPG from not getting enough "exercise. "

Really? I drive like grandma 98% of the time, but my mileage has only increased.



Ryan

 

[brods]

Lower altitudes generally equal denser air, which is harder to move an object thru. This translates a power cost that shows as mileage decrease. Cool air acts the same way at higher altitudes. It is denser and even though the barometric pressure is less, it still requires more power to to move thru it.

Thick or thin air, I just figured the effect was so small as not to be of any concern. After checking out the info on this site http://mb-soft.com/public2/car.html and crunching some numbers, it seems that thicker or thinner air can make a noticeable difference to aerodynamic drag and mpg, especially when driving a brick. Good observation Cerberusiam.



Using the “Physics In Automobiles and Trucks” article I used the approximate truck weight (7500 lbs) times 1. 8% for the tire rolling resistance at 65 mph, which came out to an estimated 23 hp. Aerodynamic drag at 65 mph, 60 F, sea level came out to approximately 33 HP. So it takes approximately 56 HP keep moving the truck down the road at 65 mph. At 3000' drag would need 30 HP to overcome and a total of 53 HP.



So, if only the aerodynamic drag changes and everything else stays the same, at 65 mph one should notice approximately a 1 mpg increase driving in thinner air at 3000' compared to sea level. It looks like about the same 1 mpg increase for driving in 100 degree air compared to 60 degree air. On paper anyway, LOL!







Some good info on tires and rolling resistance:

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=29

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=73&currentpage=29

During stop-and-go city driving, it's estimated that overcoming inertia is responsible for about 35% of the vehicle's resistance. Driveline friction is about 45%; air drag is about 5% and tire rolling resistance is about 15%.



Overcoming inertia no longer plays an appreciable role in the vehicle's resistance during steady speed highway driving. For those conditions it is estimated that driveline friction is about 15%; air drag is about 60% and tire rolling resistance represent about 25%.

 

[brods]

This works well with a normally aspirated gas engine and has exactly the opposite effect on a diesel. Adding cooler denser air to a combustion event will REDUCE power not increase it. The same will happen if if the humidity is high and there are too many water grains in the air. A diesel combustion event relies on a stoichiometeric balance to create the optimal power. Change the mixture and power drops. In the case of more dense air, the fuel burns out before it can reach the higher temps to create maximum power. In addition the denser air takes more to heat thereby reducing the amount of energy available to convert to power.

You lost me on that one. I thought diesels basically ran lean of stoichiometric most of the time since they do not control the intake air volume. Applying what you said, a more efficient aftermarket intercooler would reduce power, not increase it! Please explain.

 

[cerberusiam]

You lost me on that one. I thought diesels basically ran lean of stoichiometric most of the time since they do not control the intake air volume. Applying what you said, a more efficient aftermarket intercooler would reduce power, not increase it! Please explain.

Stoichiometric balance is controlled by the injection event, not intake air volume. The balance is slightly lean in most current diesel engines for emissions reasons to keep the cylinder temps and pressures down.



Disregarding all other factors, if you add more air than the injected event is calibrated for, what happens? Power drops becuase more energy is used up heat the extra air therefore less is available for conversion, rpm's drop, etc. Its like throwing a shot of nitrous into an engine with no extra fuel. The balance is out and will automatically adjust.



In practical applications you just use a little more throttle to compensate. Its a minor adjustment and by itself not a big thing, but, you add up enough little things and the sum ends up being significant.

 

[betterthanstock]

Stoichiometric balance is controlled by the injection event, not intake air volume. The balance is slightly lean in most current diesel engines for emissions reasons to keep the cylinder temps and pressures down.

Slow down there. Diesels are way, way ,way lean of stoichiometric. At idle you are at over 100:1 air fuel ratio.



http://www.cummins.com/au/pages/en/products/dodgeram/faq/index.cfm



Stoichiomety only applies to gassers, where fuel is premixed. Therefore, an engine needs the throttle to create a vaccuum to limit the amount of air/fuel and thus keep rpm and power in check. Leaning out a gasser too much, may mean that there will be regions below the flammable mixture limit. If that happens at the sparkplug, you got total misfire, if it happens elsewhere, you got partial misfire. A gasser, if leaned, will first burn more efficiently, which will cause higher EGT and even possibly damaged exhaust valves and pistons. It will pollute more NOx but way less CO and HC (just like a diesel). Honda had the CVCC engine, which imitated a diesel with its localized rich combustion zone around the sparkplug, with a second smaller intake valve. Direct injection gasoline engines are making a comback, with mazda, audi, ford, etc.



With a diesel, the mouth is wide open, and it contains only air. At the time of the injection, the air is heated by the compression, there is no spark plug. So as soon as the fuel droplets hit the hot air, they ignite. That way, the mixture is very rich in the injection zone, and zero away from it. Fuel can burn much more completely, since there is an abundance of oxygen. Hence the superior fuel efficiency of diesels at low power levels (in addition to the lack of pumping losses across the throttle plate, and the higher compression ratio, and higher BTU of fuel).



The mixture in a diesel will never be uniform, and if you try to even approach stoichiometry, it will not have time to mix completely like a gasser, and you get smoke. Go on Cummins site and check out their pictures of the injector pattern flame, showing, rich, and lean regions, and pollutant formation around the spray pattern.



With the diesel, there is always excess air, and excess air cools the combustion, and keeps things from melting. With a gasser, excess gasoline at WOT cools the engine and keeps things from melting. Very expensive way to cool an engine.

 

[CUMMINZ]

Better milage

The single best thing you can do to a DC is do everything you can to increase and ease the air flow into the engine. Make sure your exhaust is the best it can be.



I made a trip from central NC to NC coast this past week pulling my 5er. Generally from where I live to the coast is downhill. Generally coming home is uphill. Take that with a grain of salt. I get 2mph better going east than I do west. That tells you how easy the terrain can effect your milage. I am convinced that 4. 10 gears are better overall than 3. 73s. (This will start another war)... I generally drive 65 and under.

 

[cerberusiam]

Slow down there. Diesels are way, way ,way lean of stoichiometric. At idle you are at over 100:1 air fuel ratio.

"Stoichiometric or Theoretical Combustion is the ideal combustion process during which a fuel is burned completely"



Air fuel ratio has nothing to do with Stoichiometric Combustion in this context. Modern diesels run slightly lean of Stoichiometric Combustion for the reasons I stated, combustion temps and pressure for emissions. This is also controlled by somewhat by multiple injection events.



"The mixture in a diesel will never be uniform"



There is no "mixture" in a direct injected diesel. The air is there to provide a catalyst base for the fuel to combust. The injection paths are design to be very uniform in such a way to support a very controlled combustion event. When the uniformity is non-compliant then you have problems with roughness, smoke, egt's, and mpg.



The subtle changes in the balance, injection uniformity, etc, as it applies to the power needed to move the vehicle and meet emissions is the difference between 17 mpg and 21 mpg over a distance. As I said before, you really can'tp oint at one thing and say "Aha!" becuase there are many interlocking factors that determine the final output.