Dirty Koala
SILVER Star
You definitely will not want 4.56 or 4.88 gears with a 6BT. Remember the torque curve of a 6BT is vastly different from a 1FZ-FE. I have 4.10 gears in my axles and am running 37 inch tires with my 6BT and I will install a 9% overdrive high range gear in the transfer case when I get around to it to further reduce highway speed RPM's.My main goal is to gain more power, my rig is too heavy when loaded (5 passengers, armor, roof rack loaded with coolers, propane tanks, spare tires etc etc ) going uphill on a highway is very frustrating I’m currently running 35 inch tires and 4.11 gears (original manufacturer size)
With the 6bt I’m hopping to get more power and torque (turbocharger will definitely help)
I’m currently deciding on the gears either 4.56 or 4.88 but honestly I don’t think the gears alone will solve my problems.
Anyways thanks for all the input guys.
Researching is painful specially when is no easy answers.
Out of all the cummins swaps, I believe mine is still the one with the most power running through the drivetrain...significant fueling and other mods when I built the motor...and more sitting on the shelf So far the drivetrain has held up with the exception of my rear driveshaft which snapped whilst climbing a 12' ledge at the end of Hole In The Rock trail...just need to not drive like an idiot when you have 1000ft/lbs on tap.
There are a bunch of us that I listed below that documented our build threads pretty meticulously here as it was all ground breaking stuff when we did them. There are plenty of other builds out there now, but these were the pioneers.
@mryanangel
@thegogglesdonothing
@Mr Cimarron
@Wheelingnoob
@cjmoon
@turbophil
@maxamillion2345
As others have said, the most common way to do this swap is to use an NV4500 as you can adapt that to the HF2AV and it can hold the power no problems. The auto can be done...at least it could when bellhousings were still available, but took a bunch more work to get it to be controllable. CJmoon and turbophil both went the auto route. Max went a totally custom drivetrain route and the rest of us went NV4500 to HF2AV.
Spend a ton of time reading how we all did it, build your plan and figure out if you really want the diesel as its a very expensive conversion. If reading how others have done it is hard research, then you may want to reconsider going down this path, as that is the easy-peasy part. Speaking for myself, I love it and will probably build another Cummins cruiser down the road...75-78 series probably.