The biggest advantage to using a 4BT Cummins, over the standard 4.0L gas engine, in a rock crawler is the peak torque delivery occurring at around 1,600 rpm compared to the 3,000 rpm peak torque of ...
The Cummins 4BT might be a powerhouse ... but you'll run the risk of wearing out the stock parts quickly if you go much higher. No matter the case, the 6BT has a lot more power than the 4BT.