GCSS

OK...
I just got 20.77 mpg with my 1998 one ton 2wd dually.
My engine is the 12 valve with 5 speed and 4:10 gears.(running empty with the tailgate UP)
I also just returned from a 500 mile trip hauling a 1952 Ford Mainline auto on a flat trailer and I got 18.49 mpg.
anyone out ther getting better mileage with 3:55s?
any gidgets and gadgets that REALLY work?
My truck has the stock muffler on it too.
cmon everyone!!! lets hear YOUR fuel saving tips!
GCSS

48snowman48

I am getting an average of about 21-22 mpg with this truck. Big open exhaust, now a #100 plate with 3k springs, aluminum wheels with 33" tires, mostly easy driving but I will get on it a few times per tank. I run empty 60% of the time on mostly country roads with plenty of hills, turns and stops. The other 40% of the time I haul loads up to 2500# in the bed. Usually feed or seed that sticks above the cab occasionally. I use a slash of PowerService cetane boost each tank.

BoostdCTD

I can tell you what doesn't help, my fuel mileage went down when I added the 105lb H2 tires/wheels (even after correction) and the DDP stage 3 injectors. I don't know if it is real or not, but any vehicle with an onboard computer for the fuel mileage highly favors coasting. My Vette suppoedly got 28.4mpg driving to work the other day... staying in a high gear and coasting a lot. It has dropped a lot since, hitting traffic and dusting my tires off.

I used to get 24mpg when I first got the truck, as it is now I can hit 20mpg but can't ever seem to cross it.

HOHN

It's not just the onboard computer that favors coasting-- reality does as well.

When you coast, you're partially reclaiming energy that would otherwise be converted into waste heat by the brakes.

I get better than typical CTD mileage, and I attribute some of that to my driving technique.

jh

BoostdCTD

I don't mean coasting to a stop, the fuel computer acts as if you go down a hill it is best to let completely off the accelerator then lightly lay back into it going up the hill. In reality I don't see a big advantage there rather than just lightly keeping it going, especially since you may very well be losing speed while coasting that you have to regain while going up the next hill.

Tate

I'll trade you for your H2 wheels then. Not sure my mileage in the 12v can get much worse. Getting less than 16mpg with it, taking in account of the bigger tires. Figured a bone stock truck would get better than that.

Currently getting 18.5 mpg with the dually. Thats with my persistant fuel leak at the #4 injector. Best I ever got was 21, that was driving at 80-90 km/h for 400 km in a snow storm.

Scotty

I reduced my speed, aired the tires to 75 psi, run in 4th in the city instead of letting the 6 spd auto shift to 6th and I do not get on the throttle as hard from a stop. I noticed when I was not setting the trans in 4th, I would get puffs of black smoke when I would even feather the throttle. I attribute this to the low low rpm in 6th. I also did some off road surgery which gained me a solid 7 mpg empty and 3 hauling.
I have now seen 19 on the overhead and a solid 18 calculated. Not bad for a long bed mega cab dually 4x4.
I drive about 5-7 mph slower on the hwy now too.

Scotty

GCSS

I forgot to mention Jim Jessup tuned the motor and put in a different fuel plate and changed the timing to 15.5 advance
I can't remember what plate he put in there I am guessing a #5?????
does this sound right?

Dartmouth 12V

I average around 21mpg with summer fuel. The best mod for me has been driving style. Slowing down from 70 to 65 on the highway netted me about 1.5mpg.

austin1972

1,790 RPMs on the highway=golden....

Doj Dewd

ahh, RPM's!! i was going to start a thread to ask this question, but this thread will do just fine:
what RPM's (for truck in sig) will net me the best MPG?
i see 1790 for a 3rd gen above - anyone have any input for a 2nd gen 24v?

thanx,
jason

Dartmouth 12V

There is no magic rpm for these engines, the best rpm depends on the load. To look at the two extremes, when there is no load, the best rpm to run is idle. However, at wide open throttle, the most efficient rpm is around torque peak or 1800rpm or so. Everything else falls somewhere in between. A lot of people don't realize that lugging is just as bad if not worse than running high rpm, both for fuel economy and for engine longevity. If you could choose any rpm to drive down the highway at, I would choose 1800 for a 12V.

The biggest factor in the mileage that these trucks get is the wind resistance. The resistance is approximately equal to the square of the velocity so slowing down a little makes a huge difference. As an added benefit, you bring your rpms down a little.

There used to be a lot of threads on the different forums about people wanting to go to larger tires to decrease their rpm and increase fuel economy. Most of these people were finding that even though they were running a better rpm, their mileage went down. The reason for this is that they increased the wind resistance(which is more important than rpm) and they increased the rotational inertia.

Look at http://www.everytime.cummins.com/eve...Whitepaper.pdf for some really good info on fuel economy. You need to keep in mind that this is for much heavier trucks with much larger engines that run lower rpm but the principal is the same.

Gunrunner

"cmon everyone!!! lets hear YOUR fuel saving tips!"

Stop driving! lol

HOHN

The most efficient RPM for a 24V is 2000rpm. This means that it takes the lowest amount of fuel to make a given amount of power.

However, this is NOT THE RPM FOR OPTIMUM FUEL ECONOMY!.

A slight increase in engine efficiency of running 2000 rpm instead of 1800rpm is NOT enough to compensate for the fact that you're asking the engine to make more power because you're driving faster.

For example, it might take 90hp to hold a steady speed of 65mph on level ground with an empty truck (1800rpm). Speeding up to 72mph and 2000rpm raises the power demand on the engine-- now it has to make perhaps 110 or 115hp to overcome total drag on the engine (aero drag, tire rolling resistance, driveline friction in axles, etc).

So, we've sped up and now we're making 110hp slightly more efficiently than we were making 90hp, but not anywhere near enough to offset the increased fuel demand.

Putting numbers to it, the BSFC at 1800rpm is about .336, but at 2000rpm it's .334. This is an efficiency improvement of less than half of 1%. But the power demand has gone up by almost 15%.

Thus, you are getting worse MPG at 2000rpm than you are at 1800rpm, despite the fact that the engine is slightly more efficient at that rpm.

The speed of best mpg is the slowest vehicle speed that allows the engine to be operated within its operating range in the tallest gear.


In my case, that's about 50mph, because I don't feel comfortable running the engine below 1500rpm in the highest gear. I typically run empty.


When towing, you may have to downshift to get the engine RPM up to the operating range needed for the load-- or you might just speed up a bit. Speeding up a bit is rarely a good option, because aero drag is terrible when towing most trailers, and it's more likely to hurt you than downshifting.

That's why I'd prefer the 4.10s if I was into towing. My truck with 3.54s forces me to either run almost 70mph to get the rpm up to 2K, or I have to downshift into 5th and drop speed to almost 50mph. The 4.10s put you in the sweet spot around 65mph in OD, and you can slow down to about 60mph and still pull OD without having to d/s.

Justin

krazykarl

I get 17 city and 24 hwy. I keep my shifts below 1500 rpm and keep it under 2000 rpm on the hwy while cruising. I also keep with the flow of trafffic in the city to stay in time with the traffic lights.