Q's on regearing

[strokefreak]

Little background first....My duallie is currently equipped with 4.10s. My job requires alot of travel. roughly 700 to 1000 miles weekly. At 70 mph i am bumping 2500 on the tach. I pull my fifth wheel from place to place but am usually there for months or years at a time. Lets say 6000 pds at the most.

My questions are...
1 What is the optimum rpm range for the 7.3 at highway speeds?
2 What gearing would suit me best for mileage and also to take some load off the engine?

I am currently running 245 70 16's.:cursing: But i will be going back to the 285 75 16's very soon.:redspotdance: Any help is appreciated.

 

[Tom S]

My very general observations is that 4:10 gears are the better choice for towing and 3:55 gears are nice when empty with reasonably stock sized tires. 3.73 (if they are available) is the compromise zone but hard to see the cost for small change. I think I am right around 2400rpm at like 72mph if I remember right with 4.10 gears. If I just had to have the best 70 plus MPH truck I would do 3.55 gears. I wanted my truck to do a lot of things I would not change.

 

[strokefreak]

i was thinking 3.73's also. But, like you i dont feel the change would be great enough to justify the cost.
SSOOO....what if i upped the tire size instead...would that help? I thought i read somewhere that 35's with 4.10's was a really nice combo.

 

[Big Calo]

Just my opinion on the matter and Ill toss this out there.

My truck currently has 3.73s in it. I want to do a gear change as well but I want to go to ~3.30. Just a few things to keep in mind, I have a ZF6 and the way I do the gear pattern in L-1-2-3-4-OD. So I do have the advantge of a low gear for taking off but I can take off in 1st while grossing about 27k.

My reasoning is that with 4.10s you have a towing beast but at highway speeds you have a fuel guzzler.

With the 3.73s in my current truck 4th, I feel, is to low to pull at say 65, wound up to tight, where as OD is to high and it lugs to much.

My dad went from 4.10s to 3.55s in his one ton and for me personally its still not in the rpm range that I want.

So I found some gearing calculators and started playing around with different ratios and the 3.30 range would put me towing in 4th at about 2200 rpm but cruising in OD at about 1600 rpm.

I havent fully researched it out but I will be trying this hopefully in the near future.

 

[strokefreak]

hmmmm. something to ponder some more. thanks for the reply bud.

 

[Powerstroke Cowboy]

Just my opinion on the matter and Ill toss this out there.

My truck currently has 3.73s in it. I want to do a gear change as well but I want to go to ~3.30. Just a few things to keep in mind, I have a ZF6 and the way I do the gear pattern in L-1-2-3-4-OD. So I do have the advantge of a low gear for taking off but I can take off in 1st while grossing about 27k.

My reasoning is that with 4.10s you have a towing beast but at highway speeds you have a fuel guzzler.

With the 3.73s in my current truck 4th, I feel, is to low to pull at say 65, wound up to tight, where as OD is to high and it lugs to much.

My dad went from 4.10s to 3.55s in his one ton and for me personally its still not in the rpm range that I want.

So I found some gearing calculators and started playing around with different ratios and the 3.30 range would put me towing in 4th at about 2200 rpm but cruising in OD at about 1600 rpm.

I havent fully researched it out but I will be trying this hopefully in the near future.

I like your way of thinking... I am doing the same thing. But just 3.55 gears. BUT I will be going to 255-85R16 tires so ( about 33 inches)

But If money lets me down the road I would like to put a GV unit in there to..

 

[strokefreak]

GV would be nice. Its is def a towing beast,and very guzzly at anything over 65. Im not looking to win races with it for sure. Im leaning more toward better mileage and less load on engine at highway speed. This whole area here is something ive never dealt with so im a little slow at the regearing part. Ill do some homework and see what comes up. Thanks for the input/ideas.

 

[Big Calo]

Heres the calculator I used. I like it because you can do 2 different ratios at the same time. Just play around with it, and see what may suit your needs.

http://www.grimmjeeper.com/gears.html

 

[strokefreak]

Thank You very much Sir!

 

[Tom S]

Just a thought but in OD slow your truck down to say 1600rpm and accelerate gentily. Is that the throttle response you want at higher speeds?

 

[Big Calo]

Just a thought but in OD slow your truck down to say 1600rpm and accelerate gentily. Is that the throttle response you want at higher speeds?

I have done alittle playing around with it. With the cruise on pulling a hill or under a slight load it is fine. Just goes down the road good with out smoking anyone out. Throttle response is fine for me because it would be on CC the majority of the time anyway.

As far as a daily application I normally stay in OD until RPMs drop closer to ~1200. I can still ease around without smoking anyonw out, mind you that is very easy on the throttle.

If quick accelleration was needed, i.e. for passing, a quick downshift would put me immediately back into the sweet spot for my truck.

 

[Tom S]

If I could chose me 70 mph rpm it would be 1900 to 2000 for all purpose.

 

[strokefreak]

thats what im thinking too Tom. I would love to have it that area when going down the highway.

 

[Tom S]

But I kind of look at it like how much money would it cost to get that. 70mph is OK still w/ 4.10 I think it is when you get to 75 or 80 that it seems a bit much.

 

[strokefreak]

Yes sir, then it really screams. For months now i barely get it over 65. Seems to be my sweet spot for fuel eco. and doesnt seem to feel wound out. Honestly, money isnt an issue if i can extend the life of the engine imo.

 

[Powerstroke Cowboy]

With 4.10.. (yes it true) at 75 to 80 on the I-State i was getting 16.4 on the average..

And at 60 to 65 I could do 19.8 and every now and then hit 20.1

At 70 I was getting 18 to 18.4 All the time..

but I was running power sevice diesel clean in the gray can.. And I would double the dose so I was getting 6 numbers better on cetane...


So with 3.55 I hope to get a little better, But the main reason is lower RPMs!!!

All this was on stock tires 235/85R16s

.

 

[SDS97_7.3]

The truck in my sig has 4:10's , Im turning 1900rpm at 65 and about 2100rpm at 70. And the sweet spot is right around 68-69ish. And was pushing 19.5mpg on winter fuel (highway only)

 

[Powerstroke Cowboy]

Auto or manual???

 

[Betarocker]

Don't expect an immediate return on expense by regearing. If you have the work done by a shop, you should expect about 15,000 to 20,000 miles of driving before you break even. The reason to regear is to optimize the powerband of the engine at the most common driving that is encountered. I regeared when I had to replace a blown up rear differential, which damaged the ring and pinion. I went with 4.10s and new 37s from 3.73s and 35s, and noticed dramatically lower EGTs and quicker response. In the winter, I run a narrow 33 tire and do not notice abnormally high RPMs as my travel speeds are typically lower.

 

[strokefreak]

I see lots (tons) of highway driving. The fuel is paid for by the company. To me it just seems that the rpms are a bit to high at highway speeds. Maybe im just overthinking it.