Yeah, I said it.

Theoretical question:
Do you get better mileage accelerating like a sane person compared to an angry person or a grandma?
I was stuck going 45mph or less for the last 200 miles and I thought I remembered reading something about staying under 2000 rpm for the break in period, so I did.

All that grandma driving got me thinking because I had plenty of time to think while I was puttering along at 45mph.

I was staying under 2000 rpm and It was taking more than twice the amount of time to get to my target speed compared to accelerating like normal which is normally 1st gear - up to about 2500 rpm, 2nd gear drops down to 2100 rpm then up to about 2300 rpm, 3rd gear drops down to 2100 rpm again then up to 2300 rpm, then fourth gear hangs around 2200 rpm and as soon as I stop accelerating it shifts into overdrive and i'm running about 1500 rpm.

Now with the poking along the rpms hang out around 1700-2000 rpm while accelerating for almost three times longer.

I would think that the extended 2000 rpm run would burn more gas than the much shorter 2100-2300 rpm run.

What do y'all think.

 

Track your gas mileage while you are doing your grandmother impression, and then, once the breakin period is over, and you revert back to your "normal" driving style, see what your numbers look like then..... See what ya get. (and I would be interested to know. )

 

I already plan on it.
I normally get 11.5-12 with the 3.55 gears.
The last tank got 12.48. That is 200 miles of 45mph and under with 30 miles of 60mph and under.

 

Does the engine operate at about the same RPM as it did with stock gears/tires? (did it EVER have stock tires? )

 

The smallest tires it has had were 255 70 17.

Level road on a wind free day with 4.10s
60mph = 1650rpm
50mph = 1500rpm
45mph = 1450rpm

Same conditions with 3.55s and the current tires
60 = a strained 1500rpm If it would stay in overdrive (a gust of wind or an incline would make it drop out of overdrive)
50 = 1500 rpm

It's nice to be in overdrive on a slight incline and be able to gas it a little bit and actually accelerate without having the transmission kick out of overdrive or staying in overdrive and losing speed.
I hit the one spot today that always makes my truck either lose speed or kick out of overdrive and I could hear a little bit of a load on the engine but I didn't lose speed and it stayed in overdrive.
So far I'm happy with the gears.

 

You have true-tracs on both axles? Does your front driveshaft turn while you are in two wheel drive?

 

With modern fuel injected cars, being genltler on the throttle has much less impact than it did in carbureted vehicles. As you've seen, that geezer-type driving got you a whopping 1/2-1 MPG increase over normal driving. Worth it? Up to you, but for me it is not.

Some guys are nutty about it, and install a vacuum gauge that they pay more attention to than the speedo. There is an efficiency window that is best monitored this way. Of course, if your vehicle has an elecrtronic throttle actuator, this practice is totally pointless, as the computer will provide optimum throttle valve opening at all times, regardless of what you do.

The biggest impact you can have is finding your vehicle's happy spot in highway criusing. This is most likely where you saw your increase, since acceleration is simply rate over time (feet per second per second) until you get to speed, with fuel usage in direct proportion. Though it doesn't break down perfectly this way, figure under hard acceleration you're using twice the fuel for half as long as gentle acceleration. Pretty much a wash, with a slightly disproportionate increase in power made vs. fuel used if you can stay perfectly in that efficiency window (7"-9" of vacuum). There is a post here https://dodgeforum.com/forum/3rd-gen...6-vs-v8-2.html (#14) that explains this and other aspects of fuel economy very well. Ultimately, though, most of us spend very little of the total drive time each day accelerating, unless you're always in the city with tons of traffic and traffic lights, so fuel economy during accelration from a stop is going to have little impact on your overall average.

Anyway, what I was saying about highway cruising having the biggest impact on fuel efficiency. There is a certain point where all the factors come together in a most ideal ratio to provide optimum efficiency. It is where the vehicle is moving at it's highest rate of speed for a given amount of fuel used in propulsion. This point is typically at a lower speed in trucks simply because they are less aerodynamic. I've found it in my own cars, with the most profound example being my 440-powered '78 Dodge Aspen coupe. That car averages 12-13 MPG combined driving, but stricly interstate and with maintained speeds of 80-90 MPH, I get slightly over 18 MPG in this 3,200 pound car with 2.76 gears and a 727. Of course, with those gears and 225/70-14 tires, it's pretty much like having an overdrive with no first gear. The '99 Intrepid I had with a 3.2, on the other hand, was most efficient between 70 and 75 MPH, despite it's better aerodynamics. Driving to Kansas behind my ex's father, we were running a bit slower and averaged 29.3 MPG. Coming home with no one to keep my speed down, I was running 85-90 most of the way and saw my mileage drop nearly 2 MPG to 27.4. It is similar with the little POS Geo Prizm I'm commuting in these days, with optimum efficiency at about 65 MPH yeilding 39.4 MPG from the 1.6l 4AFE engine mated to a 5-speed manual.

Of course, there are other factors that matter a great deal, such as rolling resistance. A highway type tire, properly inflated and OEM size, is going to show you significantly better economy than an oversize all terrain or aggressive mud tire, particularly if they are run at lower pressure.

Ultimately, though, as much as I love the LA/Magnum engines, fuel efficiency is not their strong suit, and that's why they went the way of the Dodo. the heavy internal parts with relatively high friction that were designed with 50's and 60's technology and materials simply translate to crappy efficiency as compared to a modern engine design incorporating mathmatical calculations in design that could scarcely be done without a powerful computer and materials our grandparents never dreamed of.

 

HeyYou, I don't know yet. I looked at the drive shaft when I got home and saw where the stamped numbers on it are, if they're in a different spot when I get to work then I will know that it does turn at full lock. I think it might but I will know for sure tomorrow when I leave work if I remember to look.

Sixtysix, the geezer driving got me 1/2-1mpg better fuel efficiency but that isn't the only factor in my increased mileage, that was the first tank of gas with the new 4.10 gears. That is why I'm going to track my mileage for a few tanks.

Those are some good points though.
In the past I've found that my truck has had the best mileage running 70 mph with the whole tank burned on the highway.

 

11.49 mpg on this tank.
Same gas station and grade of gas.
Pretty much the same roads driven.
Getting up to 60mph for the tank.
Still around 2000 rpm while accelerating.

 

11.49 IS ABOUT all i get out of the guzzler 4.10's 33/12.5/16.5 driving like a raped ape stole it.......