So I've been day dreaming about building the ultimate 390 truck engine. One that would have way more than enough power for my truck but also last a really long time.(like another 40 years lol). Today I remembered that my friend use to have an old f500 or something with the 391 engine out in his junk pile. So I've been doing some looking. I have read that the FT blocks had heaver cylinder walls and I higher Nicole content. This sounds great for my longevity goal. The FTs also had a forged crank which while not needed would be super strong so it would not be a concern. from what I have found on the internet either the crank would need turned down and dressed with 390 front trim ( I can see myself smoking the dollar bills now) or the giant front trim from the 391 would have to be used. I also
read the FT has a different water pump. What I'm wondering is if the crank is turned down and the 390 front trim is used can a regular 390 water pump be used? While the FE blocks and parts are only gaining popularity i bet in 20 years no one will know what a FT is.Then there is having to bush the
distributor hole and swap the 390 top end on. Another plus if I could this would be the ability to run a monster clutch which would be great since this is a 4x4 truck that gets used as such. I know the 391 is balanced on the flywheel and that would take some work to balance correctly one the crank was machined. Could you internally balance the crank and then "unbalance" the flywheel? I'm sure by the time all the machining was done I could build 4 390s for the same price but it's still fun to think about.

 

Stupid auto correct. I meant nickle content not Nicole.

 

I would like to hear more on the 391 as well. I just bought a 59 F250 4x4. It has a rebuilt 391 in it. I know the 391 was very popular in the medium duty trucks, but I am not sure why the would build a 391 instead of a 390? I would guess the 391 has double the torque if the 390, but would it have half the horsepower??

 

The 390 and 391 have about the same power, the reason i was looking at using the 391 parts was that they are slightly more heavy in construction so they would last longer. I was planning on putting an entire 390 top end on the build and only retaining the block, crank, and few other pieces. Haven't found much info on any of it though

 

I have also heard that 391's use the same bore casting's as 428's so they could be bored .080 over to a 406/428 and then another .060 like the 406/428 can. Is this true?

 

With a heavy duty bottom end like that the 391 sounds unstoppable. Would a set of 428 heads add to the top end power even more?

 

The block might be a heavier, stronger piece, and the crank is steel. But, the crank has the large snout and thicker flange in the back. This won't play well with FE flywheels, front covers & pulleys. You can have the crank turned down to FE specs, and you'll have to figure out a pilot bushing for the larger opening in the FT crank as well--all as you note in your OP.

428 heads, unless they are the CJ or PI heads, are the same as 390 car heads.

FE Quick Facts - Mustang & Fords Magazine

FE Cylinder Head I.D. and Application Chart

It sounds good, but I don't know if you are going to get the return on investment. A carefully assembled standard 390 with the hardened seats, maybe a roller cam set up, good clearances and good oiling should last nearly forever, or 150,000 miles, whichever comes first....

Put another way, the block and crank are usually the least of your worries in making an FE last a long time.

 

well turns out that truck got scrapped awhile ago so its really a mute point now. I am interested in hearing any more info on building a motor out of a combination of parts though. Mostly just for curiosity sake and future reference.

 

It's MOOT point. And it's also a moot point to build a 391 and think it'll last any longer than a well built 390 will. The FE cranks were never known for being weak. The forged steel crank isn't going to last any longer than the cast one will, unless you're ACTUALLY going to pull stumps with it. Nor will the block be any stronger for 90% of all applications (like stump pulling) The 391 was also never intended to rev as high as a 390 does. They were equipped with a built in governor on the carb to prevent it reving too high. Just build a 390 and be happy with it. Take care of it, don't abuse it and it'll out last you.