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As you stated if you dont like it, it can be remedied later. Youre not lugging your engine at 1600rpms, actually states 4bts peak torque of 265ft-lbs at 1600rpms in every 4BT 3.9 Cummins manual I have, so I dont know where this 1800rpm peak torque number keeps coming from. The reason most here like a little more rpms on a 4bt is it smooths out vibrations a bit. And it does.

Ive tig welded diff housings and C knuckles to tube with very clean metal, a preheat and 1/8" ER70S2, alternating 180*.
 
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Discussion Starter · #42 ·
Ok thanks for the advice!! I still think I’ll keep them for now and see what it feels like. I would rather regear once I’ve had a chance to test it. It’ll also keep me making progress on the overall build. But now I have a brilliant explanation as to why I might be a bit low.

Yep. 19Feb2009. 3.55 (39-11 stamped gear counted to be 100% sure)
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Discussion Starter · #44 ·
I’ve been methodically planning out the whole drivetrain location and I’m curious if you folks have any resources that you like in particular. I’m going to do this right and the challenge is that I am starting with a stockish frame and an entirely new drivetrain and suspension. Here’s where I’m at.
Once I have the axles cleaned up and ready to accept trusses, links, and steering I will dirty assemble everything for location setting (duh).

1. Bolt engine and trans/tcase together and drop in the approximate spot in the frame. I have the body installed but the engine won’t have all the accessories so I’m going to have to either guess or wait until I have things like the radiator and fan to do proper location. I’ll have the turbo on.
2. Install wheels/tires on axles and align them under the frame to help set ride height. I could put them on jack stands but they may be a bit off if I can’t match the tire radius. I may still have to if I can’t get the axles to stay put. I will determine caster and pinion angles at this point as well.
3. Further adjust engine/drivetrain location to get a convergent and practical driveline angle and length. I’ll be taking into account the anti-squat, roll center etc. and the steering as I go thru this. I’m not sure yet what my wheelbase target is but it will be larger than stock for sure.
4. Links and coils will be set after. Cycling for clearance before coils. Then tear down for any welding that can’t be done in situ and the obvious rebeautification of the build before final assembly.

I haven’t been able to find a write up or thorough video for anything like this to give me pointers. Lots of beautiful pics and some detail but not everything I may need. There is a book on off-road vehicle dynamics that I may pick up on Amazon but I’m guessing it won’t cover some of my particular issues.
Thoughts?
I appreciate any suggestions. Thanks!!
 

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As you stated if you dont like it, it can be remedied later. Youre not lugging your engine at 1600rpms, actually states 4bts peak torque of 265ft-lbs at 1600rpms in every 4BT 3.9 Cummins manual I have, so I dont know where this 1800rpm peak torque number keeps coming from. The reason most here like a little more rpms on a 4bt is it smooths out vibrations a bit. And it does.

Ive tig welded diff housings and C knuckles to tube with very clean metal, a preheat and 1/8" ER70S2, alternating 180*.
Red, might add this spec sheet to your collection. Comes from a little company named Cummins. This is the 105 HP model and it says peak torque is 260 lb ft @ 1700 RPM. The peak torque point can vary depending on CPL number due to different cam grinds, timing, or injection pump. The power curve is pretty well flat in the 1700-1800 area which is the reason 1800 RPM has sort of become a standard. If you want to go by the book then it would be 1700 RPM.

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Red, might add this spec sheet to your collection. Comes from a little company named Cummins. This is the 105 HP model and it says peak torque is 260 lb ft @ 1700 RPM. The peak torque point can vary depending on CPL number due to different cam grinds, timing, or injection pump. The power curve is pretty well flat in the 1700-1800 area which is the reason 1800 RPM has sort of become a standard. If you want to go by the book then it would be 1700 RPM.
1800rpm is a design point because you can generate 60Hz AC with it. In my part of the world we run 50Hz AC power and generators have to run at 1500rpm (diesel) or 3000rpm (petrol/gas).

Lugging IMO depends on how smoothly you can run. To run a big 4 cylinder diesel at low rpm you need a heavy flywheel and smooth driveline. My 4BD1T had a very light flywheel (much lighter than Cummins 4BT) and I added 6kg of inertia ring to it with good results. It dropped the rpm I could smoothly run in top gear from about 1600 to 1400. But only with light load.

I've been in an Isuzu truck with a V10 diesel that would cruise at 800rpm. Lots of cylinders makes everything smoother:
 

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Discussion Starter · #47 ·
Plan this week is to finish prepping the front axle, tack the steering box in place, and probably starting the rear axle. I’ve figured the best way to set my approximate ride height is to add the radius increase from the stock tire to 38” to the height between the axle center and the bottom of the frame.
Then I can plumb bob the pitman to see how far forward my front axle might sit. Rear will sit such that the 38s will sit about two inches past my rear bumper. This is all preliminary and will help me when plugging in numbers in the 4-link calculator.

I bought some stuff from Barnes 4x4.
D60 high steer kit and brake brackets for Sterling:
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Sterling truss:
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Also found a D60 seal kit from IDK where but it was a really good deal:
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Discussion Starter · #48 ·
Did a first pass of the welds for the front axle. I’ve never welded nodular, never welded this machine with 240V, and it’s cold so I wasn’t sure how my beads would hold up. A bit ugly but a second gap full pass and some smart flap wheeling will bring it out just fine. Feeling much better about welding the high steer arms.
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