Howdy all
I got a 1967 F800 with a 391 and 5 speed, i wanna change to a 1972 460 engine on propane, but i dont have a trans to go with it. I want a 5 speed with over drive, but dont know what the options are or what to look for so i get the right clutch and imput shaft.
Other option is to just over haul the 391 and go propane and just swap rear end gears.
my problem is i need more speed, right now im 3600 rpm at 60 mph with tall 22.5 tires i dont think when i slow down the 391 on rpms i will have enough power. But with a 460 at 2500 rpms at 60 mph i should be more then fine.
not to concerend with fuel milage right now i get 4.5 mpg at $3.10 gas
with propane i will be 4.5 mpg at $1.80 gas sound like a great idea and im used to running propane tractors and pickups so thats no big deal.
Just wondering if you guys had any ideas
thanks
Shawn

 

spendy tranny, but id look for a zf-5 speed out of a 90's f250/350. itll have overdrive and is built for a truck.

 

The ZF 5 speed will bolt up to a 460 but the 5 speed is not rated for the F-800 32,000 GVWR truck. The 460 is not up to the task either. Maybe find a lima engine for the truck its in the 385 series witht he 460 but has 370 cubes and is a heavy duty engine. They also had better transmisson options. But the best way is to just get a new 391 FT for about 1,300.00.

 

the 460 is better than the 370... the 370 would have the same d3ve heads as the 460, same engine family, bigger bore and more stroke. it would also be a significant power increase over either the 391 or the 370. if you want you could look for the 429 truck engine- it would be a better choice than the 370. the 385 series ft engines also have big (10 qt i think) oil pans. as for the zf not being rated for the gvw thats true, but with as low as the rear gears are it doesnt matter.