what is the prime RPM

[RLDSL]

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....

I don't care how much snow is on the road, with 16 k shoving you down, once you start down Sherwin grade, gravity is taking you to the bottom weather you like it or not there's a reason they have those 55 gallon water drums every 1/4 mile on the north bound side of that road, that sucker is steep.

 

[93turbo_animal]

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

well one of us has something wrong my 93 has 4.10s and I turn 2000 rpm at 60

 

[Clydesdale]

I don't care how much snow is on the road, with 16 k shoving you down, once you start down Sherwin grade, gravity is taking you to the bottom weather you like it or not there's a reason they have those 55 gallon water drums every 1/4 mile on the north bound side of that road, that sucker is steep.

Id give you that... was pissed that night when the plow trucks turned around, enjoyed following them... laughed at a Tahoe that blew by me at 50+... never rolled it, but his tire tracks fishtailed many times....!

 

[freebird01]

well one of us has something wrong my 93 has 4.10s and I turn 2000 rpm at 60

is yours an auto or 5spd? i got a ZF 5spd....65mph is 2250 rpm on the nose in 5th gear

stock t-case and 3.54 gears...if im feelin any better tomorrow ill crawl under the back of the truck and scratch the crud off the axle tag


*edit*

whoops...just read your sig....5spd....i dunno man....as far as i know my truck has the original axle gears...and i know the trans and t-case is original. im only the 3rd owner...i know the guy i got it from was too stupid to change axle gears and he bought it from an older gentleman that used it to pull a 5th wheel camper and had everything done to it at Diesel Services in Reading,PA. Nothing I have seen so far tells me the gears have been swapped...

 

[david85]

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.

What is your current transmission and gearing?

Advancing the timing will NOT help fuel economy, I've been there and it did more harm than good, although it SEEMED to be a bit more responsive. You want to time the engine for as little exhaust smoke as possible. Thats how I was able to get the numbers I posted. Gearing is only part of it.

 

[Shadetreemechanic]

is yours an auto or 5spd? i got a ZF 5spd....65mph is 2250 rpm on the nose in 5th gear

stock t-case and 3.54 gears...if im feelin any better tomorrow ill crawl under the back of the truck and scratch the crud off the axle tag


*edit*

whoops...just read your sig....5spd....i dunno man....as far as i know my truck has the original axle gears...and i know the trans and t-case is original. im only the 3rd owner...i know the guy i got it from was too stupid to change axle gears and he bought it from an older gentleman that used it to pull a 5th wheel camper and had everything done to it at Diesel Services in Reading,PA. Nothing I have seen so far tells me the gears have been swapped...

The guy pulling the camper switched your gears? They sound like 4.10s to me. Thats where my dads psmoke with zf5 and 4.10s runs. My 3.55s don't hit 2000 rpms until above 70mph.
Try jacking it up and count the wheel revolutions vs driveshaft. I bet the driveshaft will make 4.1 trips around.

 

[zukinut]

zf-5 with 4.10s i get 15mpg at 65 roughly 2300rpms. Im doing 54mph at 2k, ill get run over here runnin 54 on the hwy.

My truck really doesnt care if its loaded or no as far as mpg. But a load sure does slow it down.

Will

 

[1989f2507.3idi]

85 at 3k lmao

 

[93turbo_animal]

is yours an auto or 5spd? i got a ZF 5spd....65mph is 2250 rpm on the nose in 5th gear

stock t-case and 3.54 gears...if im feelin any better tomorrow ill crawl under the back of the truck and scratch the crud off the axle tag


*edit*

whoops...just read your sig....5spd....i dunno man....as far as i know my truck has the original axle gears...and i know the trans and t-case is original. im only the 3rd owner...i know the guy i got it from was too stupid to change axle gears and he bought it from an older gentleman that used it to pull a 5th wheel camper and had everything done to it at Diesel Services in Reading,PA. Nothing I have seen so far tells me the gears have been swapped...

according to my door tag I have 4.10s and I run the same RPM's as my 96 which it states it has 4.10's too

 

[trail junkie]

What is your current transmission and gearing?

Advancing the timing will NOT help fuel economy, I've been there and it did more harm than good, although it SEEMED to be a bit more responsive. You want to time the engine for as little exhaust smoke as possible. Thats how I was able to get the numbers I posted. Gearing is only part of it.

Stock trans for a 92, I think 4eod or what ever auto. 3.73 gears. Dosent smoke to bad, just when I get on it and just for a quick bit.

 

[david85]

Stock trans for a 92, I think 4eod or what ever auto. 3.73 gears. Dosent smoke to bad, just when I get on it and just for a quick bit.

Theres nothing wrong with that gearing/tranny setup or your cruising RPM.....

If all you're getting is a brief puff of smoke when you tromp on it, the timing should be 'about right', as long as its clean right up to about 75% power if you throttle up gradually and the boost keeps up.

What size tires do you have?

Is the truck 4wd?

Fan clutch disengaging when it should?

Do you have a canopy on the truck?

 

[trj]

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.

What size tires are you running and what is your rear axle ratio?

 

[david85]

What size tires are you running and what is your rear axle ratio?

Stock 235-85-16 tires and 3.08 gears. The E4OD has a 29% overdrive ratio that gives about a 2.18 final drive gear ratio in top gear.

My numbers are based on personal experience as well as numbers posted by others with similar trucks over the years.

 

[trail junkie]

Theres nothing wrong with that gearing/tranny setup or your cruising RPM.....

If all you're getting is a brief puff of smoke when you tromp on it, the timing should be 'about right', as long as its clean right up to about 75% power if you throttle up gradually and the boost keeps up.

What size tires do you have?
235-85-16 I think, have to look for sure
Is the truck 4wd?
No
Fan clutch disengaging when it should?
No, spinss at all times, and free wheels a bit when shut down. I know it needs replacing, would this be part of the problem?Do you have a canopy on the truck?
Topper

Answered

 

[trj]

Stock 235-85-16 tires and 3.08 gears. The E4OD has a 29% overdrive ratio that gives about a 2.18 final drive gear ratio in top gear.

My numbers are based on personal experience as well as numbers posted by others with similar trucks over the years.

I have been very interested in the idea of having 2 top gears as you have apparently done, one for towing and the other for running empty. My tranny is a ZF5 and the overdrive ratio is .77 Do you think the 3.08 is too tall for this setup? I am running the same tires you are.