Which axles should i run?

[GoldenEagle36]

welp, im back... i got a frame from my buddy thats got 14k original miles on it, and i can start my dream build. Cummins 4BT in between the frame rails of a 79 CJ7 frame. i have everything some-what sorted out but the axles. i dont want to run a 30 front and 20 rear... but im torn between 44s and 60s.... its going to be an often wheeler and a regular driver.... but i just dont know what i should really run... Any suggestions?

 

[73CJ]

44s can run 36s & 38s with common sense and hardened shafts.

60s for a big v8 and hard wheeling.

 

[Jimbos76cj]

Go 60's the amount of torque your gonna get from the 4bt will twist up a 44.

 

[BusaDave9]

I would run 60's but I would also narrow them down. Don't run full width axles.
Also how are you fitting the Cummins in there? What tranny? What Transfer Case ? Adapters?

 

[GoldenEagle36]

I would run 60's but I would also narrow them down. Don't run full width axles.
Also how are you fitting the Cummins in there? What tranny? What Transfer Case ? Adapters?

The 4bt is about as long as the 4.0... It's 3.9L. They claim the swap is just as easy as a Chevy... But I want fuel milage and I want to roll coal in a Cj... But I plan on the 4bt(built), NV4500 out of a dodge or chevy, and I may use a 3/4 ton Transfer Case ... I wanted to run 60s. And Jeff Daniels makes bell housings for the 4bt to adapt to ether a chevy NV4500 or a dodge.

 

[tarry99]

welp, im back... i got a frame from my buddy thats got 14k original miles on it, and i can start my dream build. Cummins 4BT in between the frame rails of a 79 CJ7 frame. i have everything some-what sorted out but the axles. i dont want to run a 30 front and 20 rear... but im torn between 44s and 60s.... its going to be an often wheeler and a regular driver.... but i just dont know what i should really run... Any suggestions?

The Cummins 4BT 3.9 (239 cu in)turbo charged diesel is rated at 105 HP @ 2300 rpm & 265 ft lbs of torque @ 1600 rpm..............hardly a ground pounder that would need axles larger than Dana 44 's at either end.
Remember torque moves the truck and horsepower sustains the movement.... The heavier the components are that your moving the more sluggish the little motor will feel.......Just my opinion!

 

[jdarg]

welp, im back... i got a frame from my buddy thats got 14k original miles on it, and i can start my dream build. Cummins 4BT in between the frame rails of a 79 CJ7 frame. i have everything some-what sorted out but the axles. i dont want to run a 30 front and 20 rear... but im torn between 44s and 60s.... its going to be an often wheeler and a regular driver.... but i just dont know what i should really run... Any suggestions?

Are you absolutely married to using the 4BT?

 

[GoldenEagle36]

The Cummins 4BT 3.9 (239 cu in)turbo charged diesel is rated at 105 HP @ 2300 rpm & 265 ft lbs of torque @ 1600 rpm..............hardly a ground pounder that would need axles larger than Dana 44 's at either end.
Remember torque moves the truck and horsepower sustains the movement.... The heavier the components are that your moving the more sluggish the little motor will feel.......Just my opinion!

I was going to try and find some 3:55s to run. And the 4bt will be built up. Not just a stock one by anymeans.

 

[Torxhead]

With the hp/torque #s that Tarry99 posted, along with the added engine weight of a diesel, where is the advantage over say a GM v8? A modified engine will have its torque range moved up to where there is no real advantage in a trail rig, but then thats just my $.02.

 

[tarry99]

I was going to try and find some 3:55s to run. And the 4bt will be built up. Not just a stock one by anymeans.

Golden.........not sure why you would want 3:55's? great on the freeway with decent horsepower , terrible off road unless it's going through a 4:1 Transfer Case ..........and power wise even with an after cooler and messing with the fuel , maybe pick up another 15-20%?
Don't get me wrong.........I think it is a cute combination, but the base motor is what it is...........more fuel , bigger turbo.........equals a lot higher RPM's to get any real gains at the wheels.

 

[Jimbos76cj]

Ive got 2 freinds running 4bts in thier Jeeps. Yes 265 lbs of torque is stock for the motor.. once you do the normal minor fuel pump/fuel pin upgrade you will be pushing alot more then the 44's can handle..

My buddies 4bt is knocking down close to 700 lbs of torque. He runs a 14 bolt rear and HP front with hardened shafts.. Ill post the mods he has when I hear back from him.

 

[GoldenEagle36]

Golden.........not sure why you would want 3:55's? great on the freeway with decent horsepower , terrible off road unless it's going through a 4:1 Transfer Case ..........and power wise even with an after cooler and messing with the fuel , maybe pick up another 15-20%?
Don't get me wrong.........I think it is a cute combination, but the base motor is what it is...........more fuel , bigger turbo.........equals a lot higher RPM's to get any real gains at the wheels.

Ill hve to find the right ratio for both on road am off road. I want a ratio with good road manners and decently good highway when I travel to butler pa for the festival, but I also want something that's gonna make it a good rig off road. And with the Chevy,. I hate Chevys. All the ones I've owned I've had problem after problem. I want to get out of the v8 world and get good fuel milage, with good torque. I already have my AMC 304 that's horrible on gas, and I don't want to relive that. Plus it's different.

 

[Jimbos76cj]

He changed his fuel pin, Maxed out his fuel flow, Heavy duty gaskets to handle the 42lbs of boost, all 4" exhaust and increased his govenor.. that was his reply for his torque numbers.

 

[tarry99]

He changed his fuel pin, Maxed out his fuel flow, Heavy duty gaskets to handle the 42lbs of boost, all 4" exhaust and increased his govenor.. that was his reply for his torque numbers.

Ask him to see the Dyno sheets......Love to see them!...............Horsepower and Torque cross each others path at about 5252 rpms.......so do the math on what kind of horsepower has to be made and at what rpm it must be running at in order to get 700 ft pounds? Point is you don't generate more Torque without bringing Horsepower along with it!

 

[Scooter402]

Well, not necessarily...

Horsepower is simply a calculation off of engine torque (the only unit of power that can actually be measured) and speed, i.e. RPMs.

Lets use 700 lb. ft. of torque for example. If an engine makes 700 lb. ft. of torque at something like, say, 3000 rpms, which isn't unheard of for diesels... It would only be making 400 horsepower.

 

[Jimbos76cj]

Right Horse power and torque cross at 5252.. do you really thing that thing runs at 5000 rpm?

You can have a high torque curve that starts off haigh and drops off at 5252. If the stock motor puts out 265 lbs of torque what your trying to say is that it must also make atleast 265 horse power?

Im really not trying to argue the torque rating of his motor.. honestly I knew the flaming was comming when he told me the number.. I hate calling bul on a buddy but can tell you that it will set you back in your seat very nicely when the skinny pedal is stomped.

I know he has put some money into the motor and after looking around the internet (has to be true) there are plenty of modded 4bt's putting out very high horsepower numbers.. No saying the original poaster is going to go crazy with his motor but why build a set of axles only to have to rebuild em down the road.. Im a one and down type of guy.. in theory.

 

[BusaDave9]

A Cummins Diesel would be a cool engine for a jeep. Yes they are not much different than a AMC 258 i6 / 4.2l by length but those things are fricken heavy.
A AMC 258 i6 / 4.2l strait 6 is under 500 pounds
A 350 Chevy V8 isn't much more. (under 600 pounds)
A Cummins 4BT 4 cylinder is 745 pounds and needs 10 quarts of oil.

Don't be surprised if your nose points down.

Here's the specs on the 4BT: http://www.cumminsdieselspecs.com/4bt.html

 

[tarry99]

Well, not necessarily...

Horsepower is simply a calculation off of engine torque (the only unit of power that can actually be measured) and speed, i.e. RPMs.

Lets use 700 lb. ft. of torque for example. If an engine makes 700 lb. ft. of torque at something like, say, 3000 rpms, which isn't unheard of for diesels... It would only be making 400 horsepower.

Scooter...........your right you can make 700 ft lbs of torque at 3000 rpm's and only generate 400 HP but it requires cubic inches and or a long stroke and what the industry calls kinetic induced inertia..........whereby you have large cubic inch motors with heavy rotating masses working at low RPMS. More weight , more twisting motion which equals more Torque!
Not hardly the case in a 4BT without some major mods......Like I said I would love to see the Dyno Sheets!

 

[Scooter402]

Tarry99,

I understand what you're saying, and I perfectly understand torque, kinetic induced inertia, rotating mass, etc., as I am a Physics major by degree. Not that I really use it much these days...Maybe one of these days though.

Anyway, I was just making a point about horsepower vs. torque vs. engine speed and the calculation therein.

I know a 4bt would require some MAJOR modification to produce numbers at that level, as no stock one could ever do such a thing.

Trust me, I would like to see the dyno sheets too. I'd love to plug a 4bt into my CJ just for the fuel economy. But that's too much time and money for me...my wife has my wallet firmly clamped shut in a vice! (among other things... )

Scooter...........your right you can make 700 ft lbs of torque at 3000 rpm's and only generate 400 HP but it requires cubic inches and or a long stroke and what the industry calls kinetic induced inertia..........whereby you have large cubic inch motors with heavy rotating masses working at low RPMS. More weight , more twisting motion which equals more Torque!
Not hardly the case in a 4BT without some major mods......Like I said I would love to see the Dyno Sheets!

As far as my buck-o'-five on the topic at hand -- a mildly modded 4bt (weight aside) would do fine on a built set of D44s IMHO. I run 1/2 ton axles under a heavily modified SBC 402. I haven't broken anything to date, but on that note, I've never been in the rocks/trails with this setup. If you had the means to build a set of 60s (preferably narrowed), that would probably be best for both potential future power mods to the engine, and weight of the vehicle (since an NV4500 is no light Transmission , nor would the choice Transfer Case be).

I believe the most recent issue of Jp Magazine had a good D60 rear buildup article...I'll have to look for it when I get home and post up if I find anything.

 

[GoldenEagle36]

So I think narrowed 60s it is!