Just bumping up to my ATS Geo's 285's I could tell I had to push a little more on the skinny pedal to get er moving opposed to my 265's, what I experienced anyways. My trucks sweet spot for mileage is at 45-50 for MPH 18 MPG's give or take that is.

 

But the gear vendors unit still is for sale according to the website.

Gear Vendors under/overdrive transmissions the most awarded auxiliary transmissions.

 

Gear vendor is sweet thing (I used to have one on old motorhome with auto and learn how to change the gears with no clutch) but $3400 would take long, long time to break even in fuel savings.

 

ive had my excursion for a week now and havent seen over 9.6 mpg on the lie-o-meter, i wonder if that meter is messed up. i expected more out of a 7.3 ps even tho its mostly 45 mph city driving! anything to check that causes low mpg? tranny seems fine to me. maybe i just push the skiny pedal to much.

 

Man there is no way other than a serious engine problem that would cause you to get 9.6 mg with a 7.3. Yeah my numbers suck, but that's a worse case scenario. I would calculate it by hand- fill it till it won't hold another drop, reset the odo, then run it until near empty, then refill it, and then divide the miles driven by the gallons of #2 you just filled the truck with. That'll give ya the actual mileage you're getting.

 

My truck with all the mods minus the f6, it got a steady 16mpg ave. Then I got the 80e tune and it got a steady 16 mpg. No change in fuel milage but the power and responce is awesome. My brothers truck bein an 01 xcab shortbed will get 18mpg on the 80e driving the same. Keep the revs below 2000 and you'll gain some from what I can see.

I like the 373 and 285 combo. I'll be upgrading the tires soon. Problem is that the wider you go the more rolling friction you have. I'd also like to try a 255/85/16. I have a set on my 95 460 truck and love them.

 

ya thats what im doing now, im doing the manual calculation, i bet that mpg gauge is messed up. its gonna take forever for my wife to run it outa fuel going to work and back tho! hehehe i dont know how good it will come out since she idles it 20 minuted to warm up evey morning.

ray

 

Also, everytime you fill it up, press and hold both buttons I think it is, to reset the gauge. On my uncles 05 Ex, it works pretty well if you do that every tank.

 

press and hold what?

 

Isnt there a mode and some other button by the display? I think you press and hold the two buttons by the display. Resets the mpg counter.

 

yes there is 2 buttons, so i need to hold them down?

 

Just go for the gusto and get on of the new 6 speed autos and drop it in there, should not be the much welding to get i to fit.
i have 285 and get 15mpg on the money, would like more.

 

I never believe the well known "lie-o-meter" with my DP Tuner, it says I'm getting 23 mpg LMFAO!!! Maybe with a 5.9 and 3.55's ......

 

For those who are curious....
I did some data logging to see how the numbers come out.
All figures are in top gear with TC locked. Stock tune, stock tires. Terrain was relatively flat. The data was purged for inclines and declines before the numbers were averaged. I will be happy to send the data log if anyone is interested in evaluating the readings themselves. (I am still learning how to use my AE as well...)

I monitored vehicle speed, rpm and volume fuel desired (mm3). The following numbers are averages for the given length of time listed.

Speed=57.3 RPM=1595 VFD=18.8 Time=33sec
Speed=60.6 RPM=1688 VFD=20.3 Time=53sec
Speed=61.3 RPM=1712 VFD=18.1 Time=33sec
Speed=64.7 RPM=1803 VFD=19.2 Time=20sec
Speed=64.9 RPM=1809 VFD=21.8 Time=60sec
Speed=66.0 RPM=1844 VFD=22.9 Time=26sec
Speed=70.6 RPM=1975 VFD=27.7 Time=22sec

 

While it's true that larger diameter tires increase the "ride height" of the truck and this in turn increases the "aerodynamic drag" and therefore increases the FWHP that's needed to travel at a given MPH ...I didn't say that ...and I also didn't say the OP would necessarily get less MPG if he installs larger diameter tires!

What I did say was...

...and this only means that the GPH fuel flow needed to produce a given FWHP depends on both RPM and BP ...so if you vary the overall gear ratio between the flywheel and the tire's contact patch with the road in an attempt to "maximize" the MPG you need to consider both RPM and BP!

For example if you want to go MPH* you need to generate FWHP* ...and by varying the overall gear ratio you can go MPH* while generating the required FWHP* at various combinations of RPM, BP, and GPH such as... RPM1, BP1, and GPH1, or RPM2, BP2, and GPH2, or RPM3, BP3, and GPH3, etc... and the question is which of these combinations has the smallest value of GPH fuel flow?

I've got a computer model that can estimate the overall gear ratio for maximizing the MPG at a given MPH ...but the answer depends on the value of desired MPH ...so let's first consider this question ...independent of the overall gear ratio ...what's the "MPH sweat spot" for maximizing the MPG?

The MPG is given by... MPG=(MPH)/(GPH) ...and if you think about this equation it's clear there must be a mid-range value of MPH that maximizes the MPG ...if you go too fast the GPH increases drastically because the FWHP increases as MPH^3 ...and if you go too slow you'll use more fuel due to the very long travel time required!

As an example of how the "MPH sweat spot" for maximizing the MPG can be calculated ...consider the following "simplified" equation which gives the GPH fuel flow versus MPH for a typical SRW 7.3L ...this equation assumes a frontal area of 30 ft^2 and a drag coefficient of 0.85 and a GCW of 7,500 lbf and a 80*F day at sea level with a barometric pressure of 14.7 psia and stock tires with recommended inflation pressure and driving on a flat road with no wind and other variables that I won't bother to mention.

GPH= {0.5}+{(MPH)/(100)}+{(MPH^3)/(100,000)}

This equation was derived by first calculating the FWHP that's required to propel the truck at a given MPH ...and then the GPH was calculated from the FWHP by assuming a "constant" thermodynamic efficiency ...so this equation doesn't include the "second order" effects that RPM and BP have on the thermodynamic efficiency.

The first term in the equation accounts for engine friction ...and the middle term accounts for rolling resistance ...and the last term accounts for aerodynamic drag. The table below gives calculated values for GPH and MPG versus MPH.

At 75 MPH, GPH=[{0.5}+{0.75}+{4.22}]=5.47 GPH, and MPG=(75)/(5.47)=13.71 MPG

At 70 MPH, GPH=[{0.5}+{0.70}+{3.43}]=4.63 GPH, and MPG=(70)/(4.63)=15.12 MPG

At 65 MPH, GPH=[{0.5}+{0.65}+{2.75}]=3.90 GPH, and MPG=(65)/(3.90)=16.67 MPG

At 60 MPH, GPH=[{0.5}+{0.60}+{2.16}]=3.26 GPH, and MPG=(60)/(3.26)=18.40 MPG

At 55 MPH, GPH=[{0.5}+{0.55}+{1.66}]=2.71 GPH, and MPG=(55)/(2.71)=20.29 MPG

At 50 MPH, GPH=[{0.5}+{0.50}+{1.25}]=2.25 GPH, and MPG=(50)/(2.25)=22.22 MPG

At 45 MPH, GPH=[{0.5}+{0.45}+{0.91}]=1.86 GPH, and MPG=(45)/(1.86)=24.19 MPG

At 40 MPH, GPH=[{0.5}+{0.40}+{0.64}]=1.54 GPH, and MPG=(40)/(1.54)=25.97 MPG

At 35 MPH, GPH=[{0.5}+{0.35}+{0.43}]=1.28 GPH, and MPG=(35)/(1.28)=27.34 MPG

At 30 MPH, GPH=[{0.5}+{0.30}+{0.27}]=1.07 GPH, and MPG=(30)/(1.07)=28.04 MPG

At 25 MPH, GPH=[{0.5}+{0.25}+{0.16}]=0.91 GPH, and MPG=(25)/(0.91)=27.47 MPG

At 20 MPH, GPH=[{0.5}+{0.20}+{0.08}]=0.78 GPH, and MPG=(20)/(0.78)=25.64 MPG

At 15 MPH, GPH=[{0.5}+{0.15}+{0.03}]=0.68 GPH, and MPG=(15)/(0.68)=22.06 MPG

At 10 MPH, GPH=[{0.5}+{0.10}+{0.01}]=0.61 GPH, and MPG=(10)/(0.61)=16.39 MPG

At 05 MPH, GPH=[{0.5}+{0.05}+{0.00}]=0.55 GPH, and MPG=(05)/(0.55)=09.09 MPG

You get the highest MPG at about 30 MPH ...you get about the same MPG at 65 MPH as you do at 10 MPH ...for highway speeds and for lower speed city driving the MPG is quite sensitive to fairly small changes in MPH ...so the mileage you get between fill ups is very sensitive to the exact MPH mix driven!

Your MPG depends primarily on MPH ...but it also depends on gearing and engine efficiency versus RPM and BP. Driving for maximum MPG requires that you chose the best combination of MPH, RPM, and BP ...and the basic practical rule of thumb is to drive at the lowest MPH you can in top gear while keeping the boost gauge as close to zero as possible!

Here's some numbers from my old truck which was a SRW F350 automatic with stock 265 tires and a 4.10 diff that I installed for towing. When running empty I could stay in OD at 40 MPH ...and my boost gauge didn't move but it started at 2 psig as the minimum reading. At 40 MPH my table predicts 26 MPG ...but I never ran at 40 MPH long enough to get a "measured MPG" at 40 MPH. At 65 MPH I was running 2,000 RPM and about 4-6 psig BP depending on wind conditions ...and my "measured MPG" at 65 MPH was about 16 MPG which agrees with the value in my table!

When running empty at 65 MPH in my Freightliner I'm running 1,625 RPM and about 10-12 psig BP depending on wind conditions ...and my "measured MPG" at 65 MPH is about 11 MPG ...which is about the MPG I got when towing with my trusty F350!