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Discussion Starter · #1 ·
First time caller, long time listener...
Can't find anything solid as to what the typical crusing rpm should be.... 1900?

Just trying to figure out what gears I need.
 

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In most cases, the engine should be run at the RPM where the torque peaks for best fuel mileage. I guess it also depends on how you define "cruising" :) .
 

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Discussion Starter · #4 ·
Alright. 4BT is 1800.

Vehicle is a 2000 Jeep TJ, 35" tires, 5.5" Longarm.

120hp 4BT version. NV4500.

Gears in it now are 4.88's. That puts me 2200rpm @ 65mph
I have the resources to swap in the stock 4.10s, which puts me 1900 @ 65mph.

I'll see how it does with the 4.88's before I put the 4.10's into it.
How long a Dana 35 will last on the streets is the other question.

Thanks for the speedy replies guys!
-Scotty
 

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i got 24~26 iirc with the a/c running full tilt at those rpm's. that gave me about a 70~75 mph cruise speed. i could run 30+mpg with it at 55mph....

i think 24~26 in a 6000+lb veh isnt that bad. then again, running like i did, i wasnt one of the "i need more power" guys.... maybe that had something to do with it.
 

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I'm planning for 1700 @ 72 with 3.07, 36's and M5R2 in 5th. That will be 1770 @ 60 in 4th. That is slower than most but I want to see how it works. This will be a relatively light rig.
 

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My truck is currently running 1800rpm @ 65mph. It does pretty good but seems to have a sweet spot at 1900. Ill be changing diffs in about a month and may rearrange things to hit 1900 @ 65. May not seem like much but its the fine tuning that gets you to the front of the pack.
Carl
 

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Discussion Starter · #9 ·
Thanks guys. I'll run the 4.88's and let you know how that goes. Est. Vehicle weight will be around 4200lbs wet.
 

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How long a Dana 35 will last on the streets is the other question.
Is this a JOKE???? hahaha, sorry, i'm just playin...sorta :)

On the streets like you asked it may last a while, but I WOULD NOT get onthe throttle. I would be hesitant to run a D44 behind a 4bt, let alone a D35. I definitely would not lock it and/or wheel it, D35's are a weak link behind a 4.0 with 240 ft-lbs, the 4bta has over 300ft-lbs stock.
 

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Alright. 4BT is 1800.

Vehicle is a 2000 Jeep TJ, 35" tires, 5.5" Longarm.

120hp 4BT version. NV4500.

Gears in it now are 4.88's. That puts me 2200rpm @ 65mph
I have the resources to swap in the stock 4.10s, which puts me 1900 @ 65mph.

I'll see how it does with the 4.88's before I put the 4.10's into it.
How long a Dana 35 will last on the streets is the other question.

Thanks for the speedy replies guys!
-Scotty
Hi Scotty;

The lower the rpm, and closer to WOT you run at cruise, the better the fuel ecomony. Of course, that greatly reduces your reserve for passing, grades, etc.

If your engine is close to stock, you can use the power curves on Cummins' website to determine power at various rpm.

For your vehicle's drag at different speeds - you can do coast down measurements.

Combine the two, determine how much reserve power you want for grades, passing, etc, add this in, and you will get the answer you seek.
 

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Hi Scotty;

The lower the rpm, and closer to WOT you run at cruise, the better the fuel ecomony. Of course, that greatly reduces your reserve for passing, grades, etc.
Actually you'll hit minimun fuel consumption with your cruising revs right around max torque. On almost every diesel this lines up exactly with the lowest point on the BSFC curve.

Going too low in rpm will lift fuel consumption, but not as severely as going too high in rpm.
 

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Is this a JOKE???? hahaha, sorry, i'm just playin...sorta :)

On the streets like you asked it may last a while, but I WOULD NOT get onthe throttle. I would be hesitant to run a D44 behind a 4bt, let alone a D35. I definitely would not lock it and/or wheel it, D35's are a weak link behind a 4.0 with 240 ft-lbs, the 4bta has over 300ft-lbs stock.
What Durango said! Also, the diesel torque is right here-right now all the time with strong off-idle torque. The gasser has the vehicle moving long before any real torque is applied. Not so with a diesel: SNAP!
 

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Discussion Starter · #15 ·
Is this a JOKE???? hahaha, sorry, i'm just playin...sorta :)

On the streets like you asked it may last a while, but I WOULD NOT get onthe throttle. I would be hesitant to run a D44 behind a 4bt, let alone a D35. I definitely would not lock it and/or wheel it, D35's are a weak link behind a 4.0 with 240 ft-lbs, the 4bta has over 300ft-lbs stock.
What about installing a Super35 kit?

-Scott
 

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I'll see how it does with the 4.88's before I put the 4.10's into it.
How long a Dana 35 will last on the streets is the other question.
I am running a d35 with 33's and with and nv4500 and a mopar 360 (375 ft lbs somewhere before 3000 rpm)

It has held up good on the street. No clutch dumping of even extreme downshift engine braking. May not sound like fun but I can bark them thru 3rd with 3/4 throttle.

I broke the ring, pinion and spiders in the same D35 (never replaced the axels) with the 4.0 and stock tires and gears...not matter how much you want to race and beat the guy next to you do not dump the clutch at 4000 rpm (dump teenager).

If you like to hammer on it of run a limited slip or locker you need to lose the D35. I am going to upgrade soon.
 

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What about installing a Super35 kit?

-Scott
just changes the weak link to another weak link, there is nothing about the D35 that is really strong enough for any of this. An 8.8 would be a decent option. if you plan to use it rigorously or turning up the power, I would still hesitate with a D44. Check out the torque ratings of the different axles, you should be able to find them with a quick google search.
 
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