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Discussion Starter #1
Ok for my swap I planned on running the 4.10's I have now with a M5R2 and 33's but do you think 35's are needed instead? to high of RPMS for the gears or what?
 

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need a little more info.

Where is your peak torque?

What is the vehicle going to see in terms of average speeds?

Do the two above match on a RPM calculator.

Ideally you want peak torque near you cruising rpm. Plug in the ratios and it will tell you. If you dont know your peak torque, post your CPL and someone will probably know it.
 

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Where is your peak torque?

What is the vehicle going to see in terms of average speeds?

Do the two above match on a RPM calculator.

Ideally you want peak torque near you cruising rpm. Plug in the ratios and it will tell you. If you don't know your peak torque, post your CPL and someone will probably know it.
Good information so far...

I like this site for calculating:
http://www.drivetraindirect.com/t_gear_calculator.htm

These suggestions only apply if the engine can actually move the weight of the vehicle with little effort. If the truck weighed, (just guessing) over 10,000 lb and had a 4BT you would have to gear for faster rpms to be able to move it down the road at your favorite speed, or get more power (larger engine). (Think of it this way, if you had a lawn mower engine in the truck, geared for peak torque at highway speed it won't go anywhere.... You need enough power to comfortably move the weight of the vehicle to be able to gear it for economy..)

So, for best fuel economy and comfortable driving engine rpm at your preferred speed, say 70 mph, should be at or 100-200 rpm over the rpm where your engine makes it's peak torque. Until you know for sure what rpm that is, figuring for 1800-1900 rpm will get you in the neighborhood.
 

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Ok for my swap I planned on running the 4.10's I have now with a M5R2 and 33's but do you think 35's are needed instead? to high of RPMS for the gears or what?
With 4.10's and a top gear ratio of .73 your going to need a tire with about 560 rev's per mile or 37".
 

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Discussion Starter #6
Ok so basicly 35's and 4.10's wouldn't do it? To high of an RPM is what I'm guessing. I do mostly driving around town not to much highway driving but once or twice everyone during the good parts of the year I drive up to New Hampshire for 3 hours. Doing I'd say 70-75 the whole way. Can anyone help me out with this stuff, I did the calcultion using that link it said like 2,300RPMS with 35's and 4.10's at 75. Is that to high, I'm pretty new to diesel so I don't really know to much but I do know a few things and I know that the RPMS are much lower usually. I figured out that if I had 2,000 RPMS at 75 with 35's my gear ratio would be around 2.73ish. Sounds really low if you ask me. I don't know where the torque curve is for this engine.
 

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I calculate,
assuming you run a 0.75 overdrive transmission,
35" tires
3.73 gears

= 70mph at 1,880 rpm
or at 75mph gives 2,014 rpm.

That should be about right for what you are trying to do. If you go with 4.11 you can add about 200 rpm to those figures. If you hardly ever drive on the interstate then 4.11 gears would probably be OK, personally I would go with 3.73, as you will find yourself on the highway more and more, and then the fast gears would be nice.

Grigg
 

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Discussion Starter #8
Ok, well then maybe I'll see what I can do. I think I'm going to stick with the 4.10's as I really don't drive the highway to much. When I do though its up hill most of the time and I'm hauling stuff back and forth so I guess it won't be to bad. What should be the best cruising speed for these engines rpms wise, also what kind of gas mileage do you guys get with these engines? I tried to get to those yahoo links in the FAQ section but it won't work for me.
 

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18-30mpg, depending on rig, weight, etc. Rpm range should be 1700-1900 for best economy, stockers are goverened @2500 unless you change the spring.
 

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Discussion Starter #10
What is the red line for these engines. I'm not talking about when does the govner kick in but I mean whats the red line on them? Also changing out the spring, is that hard? what rpm should it be put to.
 

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Stock governor is the redline esentially. It defuels the engine so you can't hurt it. Lots of people switch to the 3200 rpm spring which costs anywhere around $15-20. The larger RPM band seems to help alot with light truck transmissions with a larger rpm drop between gears.

I plan on changing my spring out but the truck isn't running yet. From what I've heard it can take a couple hours to change out if you are really slow and careful. Probably less than an hour for someone who's done it before.

There are also springs available for even higher RPMs but those also require changing out valve springs to stand up to the speed.
 

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What is the red line for these engines. I'm not talking about when does the govner kick in but I mean whats the red line on them? Also changing out the spring, is that hard? what rpm should it be put to.
The Maximum overspeed (Cummins words) is 3750rpm, but using that extra 1000 rpm, will hurt your fuel mileage and longevity.
 

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Discussion Starter #13
ok so on my 3.0L right now my rpm range is from 1,000-5,500, on the 4bt its 1,000-3,700 then. Doesn't seem like a lot of RPM range to plan in. New valve springs will let me to get those higher rpms. I understand that the higher rpms will decrease gas mileage but I just wanted a little more RPM range thats all.
 

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Driving a diesel is different than driving a gasser, you don't need high rpm, you've got TORQUE ;)
 

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ok so on my 3.0L right now my rpm range is from 1,000-5,500, on the 4bt its 1,000-3,700 then. Doesn't seem like a lot of RPM range to plan in. New valve springs will let me to get those higher rpms. I understand that the higher rpms will decrease gas mileage but I just wanted a little more RPM range thats all.
No, the rpm range of the 4B (according to Cummins) is 850-2500 (on the governer), it's not a gas motor, it's designed to turn slow.
 
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