Posted by Charlie on November 11, 1998 at 12:08:27:
In Reply to: Cummins B3.9 in WM300 posted by Joe on November 10, 1998 at 20:58:32:
It would be a fantastic swap! I'm just finishing a Hercules DT3.7 into a B1PW. There's about 3/4" behind to block to the firewall and ~2.5" between fan and radiator. Since the radiator in the WM300 is 2" further forwards, you should have lots of room. I did not need to put spacers under the front springs to clear the oil pan re the diff, but I did put in a new set of front springs with ~2.5" more arch. The NV4500 is a good choice for this conversion because of the steep 5th gear (0.74:1 in the 5.61:1 1st gear versions: all dodge and newer GM models), giving 4.32:1 with 5.83s and 3.61:1 with 4.89s. Some of the higher HP 4BT ratings have peak HP at 2500-2600 rpm. If you are going to keep tires in the 36-37" range I'd advise 4.89s; I wouldn't keep 5.83 unless 41" or taller tires are contemplated.
Watch the length on the NV4500: it's 18-20" long, at least, in the 2WD configuration needed to keep the divorced transfer case. So you're going to want to mount that engine as far forwards as possible with only 1.5-2.0" clearance between fan and radiator. Be sure to get a rear sump version, also ask Cummins to set governed rpms as high as safe.
You won't lack for power.
Charlie