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How can I get better MPG on my 2004 8.1 liter 2500 A/V w/ 4.10 gears

roygbiv

Full Member
Joined
Aug 3, 2004
Messages
11
???
Hey does anyone out there have any ideas what I can do to get better gas mileage on my A/V. I was thinking about replace the tires with a 285 instead of a 245 to bump down the RPM on the highway. Any other sure-fire
mileage hits out there?

Thanks
Roy
 
roygbiv said:
???
Hey does anyone out there have any ideas what I can do to get better gas mileage on my A/V. I was thinking about replace the tires with a 285 instead of a 245 to bump down the RPM on the highway. Any other sure-fire
mileage hits out there?

Thanks
Roy
I was thinking of doing the same thing, but i'm gonna wear out my stock tires first, another thing you can do is change all your oil based fluids to Royal Purple synthetic oils, in both front and rear axles, transfer case, and transmission. :B:
 
Good Idea!!!

I totally forgot about that.

I've use to race NHRA stock cars and in that class we use to look at everthing in the car and every little bit count. Synthetic Oil was what we used to gain an advantage.

Thanx
Roy
 
I have a 2002 Av that is a 2500 with the 8.1 in it.  One of the things that helped with my mileage was the gear ratio, 3.73.  The one thing that helped a lot was having a custom duel 3" exaust.  I put a high flow air filter instead of the stock.  As far as the tires go, mine came with the 245 75R 16.  I switched to the 265 75R 16 and was somewhat pleased.  Now I am trying a 235 85R 16.  They are just as tall as the 265, but not as wide.  Nice thing about it, they are much cheaper and you have a lot more options.  With these changes I'm up to 16 mpg on the interstate, compared to the 9 mpg that I was getting

Best of Luck!
Clay91
 
Pull a fuse out for one of the injector banks. A poor man's DOD. >:D
 
K&N air filter.  And synthetic.  Royal purple is nice but I know someone who could get you a good deal on amsoil.  :wave:
 
In order of effectiveness:

1) Lower your RPM (via gears or tire diameter)
2) Custom tune (lean out your Air/Fuel and/or add timing)
3) Exhaust (straight through like Magnaflow)
4) Intake (some are better than others)
5) Skinnier tires (less rolling resistance)

I doubt going from 245's to 285's is going to help much, unless you also increase the aspect ratio (i.e. 65 series -> 70/75 series).

Be careful about using synthetic in your differentials, transmission, etc.  Not all systems can use synthetic (i.e. Eaton LSD's cannot use synthetic, and it is not recommended in most transmissions).  Check to make sure.
 
Naked AV said:
In order of effectiveness:

1) Lower your RPM (via gears or tire diameter)

not true......

engines burn fuel at different rates based on HP draw and engine RPM...

the curve looks like a hump where the best efficiency is in the middle......one has to know where this point is to know whether lower engine RPM is the correct thing to do....

The best way to increase MPG is to decrease the HP demand of the engine...

Ie...turn off AC....reduce truck weight....improve aerodynamics....etc etc etc....

 
Absolute truth?

If you're trying to increase your mileage to save money in gas, you're probably wasting your time. Most mods that would have any significant effect will cost you *far* more than the fuel saved.

As for decreasing rpms, there's less difference than you might think. I went from 3.73 to 4.10 and the difference in mileage (non-towing) was so little as to be statistically insignificant (I lost 0.3 mpg). On the other hand, while towing, I *gained* 2mpg. Even so, if I was doing it to save money, it would have been a waste. You can buy a lot of gas for what new gears cost.

And specifically with regards to increasing tire diameter? My best bet is you would *lose* gas mileage. Anything you gained in decreased rpms would be more than offset by the increased wind drag.

Want to save gas? Slow down, and go gentle on the throttle when accellerating. You'll save more gas than with any other mod, and it won't cost you anything.
 
You can achieve better gas mileage without costing more money.  The synthetic I sell cost less than regular oil and will improve gas mileage.  As far as the rest goes, you are probably better off to save the money if you are comparing saving fuel vs initial cost.  However some do eventually pay off, plus you get the added power.  >:D
 
msheldon said:
Want to save gas? Slow down, and go gentle on the throttle when accellerating. You'll save more gas than with any other mod, and it won't cost you anything.

Kinda points to my brick under the gas pedal mod huh.....

the true way to save gas.....hehehehehe
 
Prime Power said:
You can achieve better gas mileage without costing more money.  The synthetic I sell cost less than regular oil and will improve gas mileage.

Y'know, I see this kind of claim all the time.

Now, I'm a huge proponent of synthetic lubricants, both in my trucks and in my bikes. I always switch to synthetic after the break-in is complete. However, if anyone actually thinks they're going to see a noticeable difference in fuel mileage with a big-block truck just by using synthetics, well, I'll be happy to give you a smokin deal on this bridge I need to unload.

Even in my bikes, the difference was hardly noticeable, and the bikes are far more reactive to performance tweaks. It does make the motors last longer though.
 
On my car I did see a 1-2 mpg increase.  On the truck I would like to say I saw a .5-1 increase but it is hard to tell sometimes at that low of amount.  Plus with all the other mods, who can really tell.  But for sure it is better for your truck.  And if you think about it, less friction, more available power so at least theoretically it should increase gas mileage.  But big truck likey gas.
 
My 8.1 gotta tow power... towing cross country? 7.5 mpg at avg 80-85 MPH.? Around 10 at 60-65 MPH. 2004 40,000 miles. 4 TRIPS A YEAR 12,000 MILES COAST TO COAST.

I could not find my calculator but:

If I could get 10 MPG I would need 512 gallons less.? Easy $1,200.00.?

As to getting 16 on the freeway... seems impossible.?

I do not understand "Custom tune (lean out your Air/Fuel and/or add timing)".? What would that do to the drivability?.?

??? Would getting a performance chip help?? ?

My state does not require smog equip (in my area) is there something that can be done... to improve milage from that direction?


 
DADDIO2624 said:
7.5 mpg at avg 80-85 MPH.  Around 10 at 60-65 MPH.
...
If I could get 10 MPG I would need 512 gallons less.  Easy $1,200.00.

Sounds to me like you already know how to reach your target, you're just not willing to do it.

TANSTAAFL (There Ain't No Such Thing As A Free Lunch) You want to move at high speeds with a non-aerodynamic vehicle, well, you're going to burn a hella lot of gas. That's just physics.
 
I think the brick under the gas pedal is probably the best way.? I recently did a comparison on driving with effeciency and the way I wanted too.? 2.5mpg difference.

I got 10.5mpg driving the way I like.? Aggressive and having fun with the 8.1.

I got 13.1 mpg driving effeciently around.

I got a 2500 and thats mostly highway miles in commuting, with a little around town.? But I doubt that any other mod is going to make that much difference.

I agree with others, if you are really worried about MPG with the 2500, then you may want to sell it and get the 1500 instead.? The 2500 is about power and added towing capabilities, not MPG.

If anyone is serious about trading their 4.10's for 3.73's in a 2500, I love to swap you.? I have an 03 2500 with 3.73's and am going to be going with a lift and bigger tires soon, so I'd love to trade, swap, or barter for the deal for your 4.10's.
 
The following is my recollection of listening to an SAE engine designer talk about HP/MPG/Mapping.

Every engine has a map of the engine abilities, efficiencies, and how it uses fuel. Inside the map is a bubble of area that you can optimize. The factors effecting it is the type of fuel, the delivery mechanism, the structure of the engine, the transmission type, the gearing of the engine, etc... If you have an engine map you can move the factors (vectors) around within the map to optimize.


So, I'm trying to get access to the engine map for a 5.3, and 8.1 just for grins and giggles. I'm imagining the map will determine what the max (theoretical) MPG of the engines can be, and what vectors have to be effected to get there.
 
Changing gear ratio will help on the highway, the lower the numbers will reduce your rpm's and you will burn less gas. I have the 373's in mine and she just chugs along on the highway, however i want to put a lift kit on my rig and 35" tires and want a set of 4.1 gears, so if you do change yours I would like to buy your 4.10's.

 
MM. don't waste your tim eormoney on the 4.1's. The 373's have plenty of power in the 8.1, you really don't need to change the gears when lifting. I have been happy with both of mine!
 
what lift/tires did you have? and did you tow with yours? i will be towing a snowmobile trailer and gear say less then 5000 pounds (truck is rated for 11000)
how about economy? i lifted my silverado with a HO 5.7 engine and 3.73 gears and when i put 35" tires on her she was  pig on gas, always to the floor to get her to move, i put 4.56 gears on her and the power came back and so did the economy.
but that's because the engine was underpowered for the truck, im running over 100Hp more inthe AV.
 
I'm with you MountainMax.  I beleive you need to change, especially if you tow.

If your truck came with the GT4 option 3.73 ratio, to keep approximately the same ratios with stock tires, you'd need to go to 4.10 if you go to 33" tires and 4.56 if you go with 35's.

If you don't change the ratio, you'll notice, especially if you tow anything substantial.
 
ygmn said:
Kinda points to my brick under the gas pedal mod huh.....

the true way to save gas.....hehehehehe
x2

I normally get 13-14 mpg around the city.  I lend my 8.1 w/ 4.10s out and the DIC always shows being down .5 -1 mpg from where it was when I lent it out.  Specifically my friends wife who normally drives a 6.0 psd.  She is used to the lag.

Don't use cruise either, that will eat up your milage.  Accelerate breifly at the bottom of hills and then let it drop a little towards the top.  Helps out a lot on mileage.  (15 mpg is my best though, but I usually use cruise on the hwy)
 
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