4BT into Bullnose Ford: How many 6BT parts can I use?
 

Hello all, I have a 1981 F-250 I want to swap a 4BT in place of the 300 I6. The truck's got a T18 4 speed, a NP208, 3.54's out back and 33" tires. Anything I haul usually fits in the bed or is under 5k lbs, the truck occasionally goes on trails, doesn't see extended highway driving over 55. I know most people usually go for a 6BT but I wanted to do minimal structural modifications and fabrications, plus the truck drives well as-is and the 4BT has very similar power in very similar places in the power curve; so I shouldn't have to regear or anything.

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I wanted to know how many off the shelf 6BT swap parts I could use to put a 4BT in my truck. Are the motor mounts in the same place? is the bellhousing the same? Do I need a different clutch or flywheel? Do I need a different fuel pump and filter?

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Many thanks!

The clutch and flywheel are definitely the same for either a 4bt or a 6bt. The fuel filters mount the same way. There are several different configurations out there, but it shouldn't be a problem to make something work.

Motor mount locations? I don't remember... it's been almost two decades since I worked at a Cummins dealer. But that's pretty simple stuff to figure out. You can't really do this swap without a welder and a drill press anyway.

I think a 4bt in one of those early 80's F150's would make a great truck. My favorite truck I ever had was an '85 F150, 4wd, short bed, standard cab, 300 I-6. Very similar to what you have here. It had the T18 transmission and 3.55 gears (this had the 8.8" rear being an '85). It wasn't fast, gas mileage was nothing to brag about... but that truck had soul. Unfortunately after 12 years of ownership, rust had finally rendered the thing obsolete. I have a GMC these days that's a better truck by every quantifiable measure... and I still miss that old Ford.

A 4Bt should be a great engine for the truck as long as you're ok with a top speed of only 55mph or so (need to do some math to get an exact number on that). An overdrive sure would be nice though. But they're not cheap.