To figure the gear ratios and speeds you need to know a few things,
Gear ratios in the axles, and any other ratios available if any.
Engine you desire to use, and the RPM where it makes peak torque.
Tire size (actual outside diameter).
Transmission OD ratio if any, or ratios for possible transmissions.
How fast you'd like to cruise on the highway.
With that info you can plug the numbers into one of the many on-line gear calculators to do the math for you.
http://www.onlineconversion.com/bigger_tires.htmFor example My truck can use 3.54 or 3.73 axle gears. Has 38" tires, a 0.80 overdrive ratio, likes 1,800 rpm and I want to go 68 mph.
A 3.73 axle ratio in OD gives me that.
Or more likely I'll use 3.54 to give 2,000 rpm at 65 mph in direct for towing, and in OD can cruise comfortably at 70-75.
There is a lot to learn and figure before starting on a diesel conversion. I suggest you spend some time browsing 4btswaps.com.
No, fuel tanks need to be vented, yes you'll need a return line as well as the pickup line.
Grigg
