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Hey Stud, I'm doing the same, only using Unimog U1300l axles instead of the smaller Rocks :happyfinger:

7000-8000#'s
Rockwells (6.72 gearing)
53" Michelin tires



A healthy 4bt will work fine
I have access to some 406's for a good price, just already have the rocks. I'd be worried about splitting portal boxes.

My 4bt has 65k and I was planning on doing the Marine tune (250hp/500lbft'sh)
 

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Hi,
I dont know how things work in the states but i'll give you an insight to how much power is enought to get the job done.There is a certain truck here that goes by the name of TATA.It uses a Cummins 6BT rated at [email protected] and 400lbs/[email protected] and with a 7.86:1 1st and 6.86:1 final drive.The truck weighs 14000lbs and the rated payload is rated at 42000lbs which makes a gross wt of 25 tons. Now pls note that trucks with similar specs in the U.S. are rated at just half the payload capacity that we have here so according to you guys it would already be overloaded, but thats not enough, here they are loaded to twice the manufactures payload rating.
Now just imagine what it would be like for a truck that overloaded at 4 times the U.S. payload rating, at about 98000lbs:nuke: going up a 25% incline in only the 1st gear.They dont use egt gauges of any sort,as usually the axle give up before the motor can, but the point here is that if a very underrated 6BT can pull 98000lbs up a hill, why do you think a 4bt that produces about 12 times more torque/wt ratio cannot work for a trail vehicle.
Also something worth noting is that since these motors produce most of its torque just off the idle, it can do without any throtle at the trails and more so ever coz of this very fact it can do without very low gearing to maintain the same speedas a v8(if a v8 has to be reved at 1400rpm at maintain a certain speed, the 4BT would not need as low gearing to do just that as it has enough low-end to keep doing that at just 800rpm).This also explain why mcinfantry's vehicle was so good at what its been doing. Another important point is that no matter how much power you get out of the motor, be it 200hp or 400hp, if you vehicle needs just a certain amount of power that to overcome an obstacle, then your engine is going to produce just that much power, not any more, so you just end up wasting fuel in a very tweeked motor.
Now ofcource,on the highway you might need more power for better acceleration, but that is another matter.
Ragards,
Brutus
 

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Welcome, Brutus.

Nice to see someone from India here!

I agree, my 4BT will be plenty strong for most any task as long as it is geared low enough. I know I could pull 25,000 lbs as long as I never take it out of first gear.

Problem is, it needs to have good HP to pull a load at highway speeds. I do not have an overdrive transmission (just the original 4 speed) and there are times that even at 10,000 lbs total (pulling a trailer) it has to work pretty hard to keep 100 km/hr, mainly while climbing hills. I installed an EGT probe in the exhaust manifold but haven't added a gauge to the interior yet. Judging by the smoke it makes to get up a big hill, I am sure the exhaust temps are pretty hot! I just completed a long trip and was only getting 15 miles per gallon on the trip.....I think it would have got better mileage with a 6BT because it would not have been working as hard as the 4BT was.
 
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