what is the prime RPM

[trail junkie]

For the best MPG in an 7.3IDI???? Just wondering what I should run on my next trip to get prime milage.

 

[freebird01]

mine is about 1900rpm (55-60mph) in 5th gear unloaded....i get 17.5 winter and 18.5 summer...if i run 65-70mph (2100-2250 rpm) i drop to 15-16mpg

thats a 250 ext cab 4x4 long bed ZF5 speed 3.54 gears

 

[typ4]

anything under 2000 is my sweet spot, 1750 to 1800 rpm personal best was 19mpg.

 

[RLDSL]

Some specs in your signature would help. these guys with the tall rear ends like to brag about those nifty fuel mileage figures. those of us with crew cabs and 4:10 rears , if we wanted to run at 1750 rpms, we'd have to ride on the shoulder with the flashers on chasing the possum pluckers

 

[k_williams1982]

Some specs in your signature would help. these guys with the tall rear ends like to brag about those nifty fuel mileage figures. those of us with crew cabs and 4:10 rears , if we wanted to run at 1750 rpms, we'd have to ride on the shoulder with the flashers on chasing the possum pluckers

That's the truth! At 60mph, I'm running around 2,400rpms. I've got a CC, 4.11 rear, and a C6 (3 speed). I want to change out to a ZF or at least add an OD unit sometime soon. Have checked my accual mpg yet.

 

[LCAM-01XA]

E4OD with 4.10s behind it, used to like 1900rpms in the summer (55mph), on long trips running empty I've seen consistent 20mpg. Now with the winter and the brew I'm feeding her, she seems to like 2000rpms more, that's about 60mph - this is actually a bit more convenient as that's how fast most 18-wheelers go, but on the other hand the highest I've seen with this cold and stuff is 17-18mpg or so... I don't mind going 55 in the summer, I just put my wooden hay stakes on so folks automatically assume it's a worn out farm equipment and just zoom by me and leave me be

 

[Shadetreemechanic]

For the best MPG in an 7.3IDI???? Just wondering what I should run on my next trip to get prime milage.

Between 650 and 750. Just don't get in a hurry. The lower the better. I have gotten my best mileage at 1500, just moving lazily along on two lanes, but I have broken 20mpg up to about 1900RPM with EO4D and 3.55s.

 

[freebird01]

Some specs in your signature would help. these guys with the tall rear ends like to brag about those nifty fuel mileage figures. those of us with crew cabs and 4:10 rears , if we wanted to run at 1750 rpms, we'd have to ride on the shoulder with the flashers on chasing the possum pluckers

my next truck will be a CC dually 4x4.... but for now ill "put up with" my low mileage 88 F250 ;p (99k)

 

[trail junkie]

I have a crew cab dully with 3.73 gears, and have yet to break 14mpg unloaded runing ~1900 rpm, I must be doing it wrong . And yes they are 3.73s I put them in.

 

[Clydesdale]

Personal best mg, was loaded to 16k (tandt) at 25mph in third (ZF) from Mammoth Ca to Mojave CA in 4 hi... truck did damn near 18...

Can't break 15 empty.. regeared to 3.73's (yeah I put the 35's on myself... ) and ... that may help, course I idle it for an hour before we go anywhere so (fricking hate cold cars, hate winter) so I get 13 ish currently unladen

 

[RLDSL]

Personal best mg, was loaded to 16k (tandt) at 25mph in third (ZF) from Mammoth Ca to Mojave CA in 4 hi... truck did damn near 18...

Can't really count that run, it was seriously downhill most of the way . Heck, you probably ran all the way from Mammoth to Lone pine for free with that kind of weight behind you. At least as far as Bishop

 

[Papabear]

need more gears the more the better as the reason why i ask alot of questions pertaining to gear sets and what fits what

 

[david85]

These are the general guide lines that I came up with:

Empty:

55 MPH : 1500 RPM
60 MPH : 1800 RPM
70 MPH : 2000-2200 RPM (depending on the size, height and weight of the vehicle, head wind, etc)

towing:

55 MPH : 1800-2000 RPM
60 MPH : 2000-2200 RPM
70 MPH : up to 2500 RPM (assuming it will even go that fast)

Turbocharged IDI empty:

55 MPH : 1400 RPM
60 MPH : 1500 RPM
70 MPH : 1600 RPM

Turbocharged IDI towing:

55 MPH : 1600 RPM
60 MPH : 1800 RPM
70 MPH : 2000-2500 RPM (again, depending on how much load)


The overall happy medium cruising RPM is about 2000. This has enough power to spare to for some extra load, but also is low enough RPM to be fairly economical.

I geared my truck to have 2 top gears instead of just one. At 70 MPH, I can pick between 2250 RPM for towing, or 1650 for cruising empty. With the topper off the truck I was getting consistently 20 MPG or better last summer. The high fuel prices may have also had a positive effect on my driving style

Personal best was 22.5 MPG averaging between 65-72 MPH. I base my calculations on the same highway going 100 miles south then the same route back home to get a good average that accounts for slopes or prevailing winds.

 

[trail junkie]

need more gears the more the better as the reason why i ask alot of questions pertaining to gear sets and what fits what

I would have to say I am missunderstanding you. When I got the truck it had 4.56s in it, at 65 I was running 3000 rpms. Let alone bad for motor, you dont want to see the milage on that. Truck has a turbo and fuel is turned up/timming advanced. All these things I thought would help my milage, but nothing. I am just starting to get frustrated with it cause I see guys on here post getting 18-20mpg, and there is no way I could touch that. Oh ya and the ford factery rebuild only has ~14000miles................not sure if that is good or bad as for my milage. Any ideas would be great.

 

[Clydesdale]

Can't really count that run, it was seriously downhill most of the way . Heck, you probably ran all the way from Mammoth to Lone pine for free with that kind of weight behind you. At least as far as Bishop

The 14" of snow fall that I was driving through, started at 11 pm, and quit at 5 am, I slept in big pine from 3-7.. made me use the raw brute force of the diesels ponies a wee bit....