I still say I drive a 2000 5.9 3/4 ton Dodge 4x4 with a six speed and 4.10 gears more often that I care to admit.

If I drive it like I drive my 6.9, the mileage is about 15 versus 12 in my IDI.

Most of that I think is from the overdrive.
Actual miles driven divided by actual gallons used over a couple week period.

Yes if you look at that stupid MPG meter in the overhead, 22 or 25 MPG is displayed a lot.
But when you use hard numbers, that display is far from true MPG numbers.

 

My truck has 2 top gears for freeway speeds. Overdrive is for light loads (1650 RPM), and 3rd gear is perfect for towing (2250), so my answer would have to be both fuel economy and towing. Most of the time its empty (especially with the recession)

For low speed manouvering of a heavy trailer on steep grades, thats what low range is for (.....and thats where traction becomes a problem). I've never had a problem getting a load moving with 3.08s though.

While it may be true that my truck is heavily modified compared to stock, it really isn't out of line when you consider the fact that the Getrag has an overdrive top gear and dodge offered their cummins diesels with 3.07s.

A 7.3L with a ZF 5 speed and 3.55s will also get in the low 20s empty, so I still don't see what the big deal is.


OK I'll try to go back on topic though, since hypermiling isn't the original point of the thread(sorry, my bad)
For horsepower mods on an IDI:

Any turbo you want (banks, ATS, hypermax, new or used),

PSD intercooler,

Code E injectors,

ARP head studs

Moose pump,

Bigger compressor housing

$$$$

In reality, for what you want, only the first one on that list is needed. A healthy turbocharged 7.3L IDI will put down over 200 Hp to the road rather easily. Once you start pushing significantly more than 10 PSI of boost for sustained periods, you need an intercooler. 10 PSI will already make your truck move rather well though and there won't really be any MPG penalty.

If you were to do everything on the list......then you're truck would almost be ready for competition. But it would get costly and its really not needed for the real world.

 

If I'm putting $40k down for a truck the least they could do is be honest with me. Its no accident that the MPG meters are OVER estimating rather than underestimating. If you want real MPG numbers, you still have to calculate by hand.

I will never buy a new vehicle for this and so many other reasons.

 

I'm not sure about smokin a buzzin dozen but I would sure hate to feed that thing.

 

four of my friends have cummins and the only way they hit the 20mpg mark is with a chip stock they are in the 12-16mpg range and thats driving nice with no load 2 of them use there trucks as grocery getters and 2 use them for hauling from time to time

 

It's a conspiracy!!! (insert shify eyes smilie)

They don't call them Lie O' Meters for nothing. I've never seen one that was very accurate. It is an instant average. The calculation and accuracy is a lot tougher in a 1 mile period, than say in 500 miles. Especially when you factor in engine load, fuel rate, and not just miles to fuel used.
Hand calculated is always the best. Heck, even those figures can be inaccurate because of the variables involved. So an average over several tanks is the most reliable number. On the highway, the L.O. Meter in my Dodge has read as high as 26. Actual numbers hover about 19.5 mpg average. And it gets better mileage at the top of the tank, than at the bottom, according to the overhead.

So with a load, you're not able to use the top gear with your E4OD? Comparing the auto OD to the manual is unfair because of the heat created in high gear, though. Not many use the OD when pulling because of it.
So comparing manual to manual:
With the torque curve on the Cummins, it is right in the sweet spot in OD with those gears. I don't think the turbo IDI with a ZF and 3.08's is going to be able to pull 5th as well because it puts it way below the peak torque.

The 1st gen Cummins 2wds are capable of mid 20's, easily. Many 4wd's are reaching the low 20's. And this is more the rule, not the exception.
Yeah, a 2wd IDI with 3.55 gears and an OD will pull 20+ mpg. But finding a 4wd IDI to even break 20 is not common.

I respect what you've done with your truck. To get over 20 mpg from a heavy, non aerodynamic, 3/4 ton truck is a feat by any stretch. That is pretty cool

Fuel mileage is less of a concern to me than being able to tow or haul anything I want to with my truck. I think the last time I actually checked the mileage on my 7.3 was about 5 years ago. I fuel off of the aux tank and don't have a meter installed.

Jason

 

Well I paid attention to the overhead readout on the westernstar I'm currently driving this trip the lowest I saw was .72 mpg and the highest was 88 mpg I think it is safe to say it will actually be somewhere in between.

 

I don't lock out overdrive when towing to save the transmission. Its to keep the engine in the right powerband since my turbo (despite my best efforts to date) will not spool more than 3 PSI @ 1600 RPM. My final drive ratio is less than 2.2:1 in overdrive, so even with gobs of bottom end torque, there is a limit to how much weight you can move with that gearing. If you were to take apart an E4OD transmission, you will find the overdrive section is actually built stronger than all the other gears in the tranny. Its other minor secondart parts that cause problems in early versions.

If I had 4.10 or 3.73 gears, I would not hesitate to use overdrive. There are times that I will tow a light trailer (~1500-3000) in overdrive if conditions permit. Truth is its rare for me to need to move more than 3500 lbs with my truck. If you think about it, big rigs drivers have to select the right gear for the right conditions. Seems only logical to scale that down in a light pickup. Why run around empty with more RPM than you need?

Actually, the type of turbo does matter here. My 088 isn't bad, but I just can't get it to boost worth much below 2000 RPM. This more than anything else seems to affect my powerband. I added a 60-1 compressor and it did help a little, but more needs to be done to get it to where I want. Header wrap is something that I would add to a list of performance upgrades for these engines, at least on the turbo plumbing. The lack of a heat shield on my turbine housing probably doesn't help either. The flip side is I have never seen 1200 EGTs so far, so with enough RPM and fuel lots of power could be possible near the top end. Otherwise, just get a newer wastegated turbo and wire the wastegate shut.


LMAO!! @ starmilt, somewhere in between alright....

 

i think its wierd you cant get no more boost than that, i know you have your truck manly set for mpg's but maybe you need more fuel?

 

I screwed around with the injector pump a while ago and am trying to get the settings back to where they should be. Latest adjustment did help, but its not there yet.

 

With a non wastegated turbo, boost below 1600 RPM is going to be low even with black rolling out the back.

A wastegated turbo can spool more agressive at lower RPM without the concern of overboosting at higher RPM.