390 VS 391 Just so i know what i am getting into.

[fe66comet]

I am thinking of picking up a 64 Ford CO with a 391 4v. Other than the obvious crank (huge snout) and bell housing pattern (385) BB, what other differences are their? I never had one apart so I was just wondering what I am getting into?

[BH107]

Almost everything is the same as an FE, including the bell housing pattern. The heads/ intake are unique, as is the front timing cover to clear the big crank snout. The distributor pilot is also larger, but there are bushings available to use an FE distributor if needed. You can put FE heads/intake on a FT engine. In fact, the 391 block can be used in an FE build as long as the distributor pilot bushing is used.

I saw your post on the O/T page. If it is a cab over it would be a C-600, and a conventional cab would be an F-600.

[KMcCullah]

Lots of differences in the rotating assembly also. The 391 is externally balanced. The 391 damper is a huge chunk of iron with cast in balancing. The flywheel also  has cast in balancing. If your wanting to use the steel crank in a regular FE, it will need to be sent to a crank guy to have the cheeks machined, nose turned down etc.
Edit: If memory serves, the 391 crank weighs around 30lbs more than a 390 crank.

[fe66comet]

Actually my intention is to leave it original, very nice original cab over truck. I would use it to haul my tractor to shows and such. I am sure a two speed axle would be a welcome addition as would power brakes. It already has a power assist steering kit installed from the dealer. The bell housing is definitely different than a normal FE. The housing is a 429/460 deal with a monster clutch and flywheel. The guy who has it has another engine just like it sitting in a barn. He said it was a 429 bolt pattern. If I ever had to rebuild it a striker kit would be nice but would require rewelded journals I would guess. I would be interested to know what kind of heads are on it but I guess I will have to get it home first. I wonder if it is a mechanical or hydraulic camshaft?

[GJCAT427]

All of the 361/391 used a large 13" clutch. The bell housing is also larger for the massave flywheel. It will fit the 390 block but the starter is moved outward to fit the flywheel. I don`t know where he says the bell is a 429/460, it won`t match up period. also the FT bell has rear mounts to fit the truck chassie. There is a 429/460 truck motor with the large clutch/ rear mount but again won`t fit the FT/FE block.

[machoneman]

I'd pay close attention to what GJCAT427 said. None of the 385 series bells will work and the motor mounts on the 391 pretty much require you cut up or fab up your current mounts to fit them, not the other way around. Lotsa work IMHO for little gain as a traditional 390FE would slide in no problemo! JMO!

[GJCAT427]

You can use the FT flywheel on the FE, BUT you must get the wheel "0" balanced. The FT has a wedge shaped weight cast into it. You can machine it down ,but it still needs to be rebalanced for the 390 to work.

[fe66comet]

I am not changing anything anyhow, just maybe an internal overall later. As far as the bell housing it will stay as is, it just looked different. The truck is a 10,000 LB vehicle so if I do anything it will be durability or torque improvements. I would consider a better camshaft and some thin head gaskets to raise compression. I think the biggest obstacle may be the lack of oil journals to the lifters maybe? But I would go flat tappet either way with a good valve job. The flat bed I am considering changing to something smaller, right now it is about 18 X 10, I am thinking more like 8X14 would do me fine and I could sell the larger bed. The drivetrain is impressively massive with the huge clutch and trans along with a monster dually read end. I would definitely like to get a 20% over divorced box from another truck. As I said before power brakes and a dual master would be for sure on the upgrade list. The power assist cylinder on the steering needs a rebuild or replacement,the seals are gone from age and it leaks like a stuck pig. The pro take off and dump cylinder are nice features as an added plus, I could add a beaver tail to the bed to load my Comet or a tractor nice and easy.