ok here it is i have a 78 f250 with a 390 in it i am putting in a 351c or 351m im not sure witch it is yet i have not picked it up yet what do i need to change or does it just drop in. any info is helpfull thanks.

 

Definitely not a drop in! You'll need a different transmission or at least a bell-housing that mates to 351 you chose. I'm not sure, but I think the Cleveland and the M are different, keep that in mind when finding parts. You'll need motor mount perches for the 351. You'll probably need a different length drive-shaft and to relocate the transmission cross-members as it's position will most likely change.

I'm sure I've missed a few other items.

That being said....WHY would you replace a 390 with a 351? If you're hoping for better mileage, don't bet on it.

 

well you will run into problems because in order to get the 390 in there now the po probably cut up alot of stuff because a 390 was not a option after 76. keep the 390 if thats what you have now.

 

well the 390 is toast lots of water in crankcase and i pulled intake manifold and there is rust on pushrods and rocker arms. im guessing its a 390 it looks like all the descriptions of the 390 and the intake says edlebrock performer 390 on it.

 

how can i tell if the head gaskets are good or bad without pulling heads?

 

you can do a compression test, the performer 390 intake fits all engines fe and ft but most likely someone swapped in a car 390 engine.

 

I think they offered the FEs in the F250/350s up until 79. I could be off my rocker again.

Anyway, it sounds like it needs to be pulled apart and rebuilt. you can find running 360/390 FE engines for a decent price. They would be a drop-in replacement for less than what you would spend adapting a different motor. Or, you could rebuild the engine you have.

is this your daily driver, are you in a hurry, what's your budget?

 

my bad, please ignore the comment about the ft engine i put that there by mistake i forgot this thread was about the 78 ford and not about the f600 dump truck. sorry.

 

try here i bought one for 1,200 www.rebuilt-auto-car-engines.com

 

I think after 77, the FE's were toast. My Motor's Truck Repair manual doesn't list any FE's from '77-'79. FT's, yes, but they certainly weren't in any F-250/350's...

 

do i nee to put intake back on to do comp. test?

 

You'll need all the pushrods/rockers assembled, but you don't need the intake...

IT'll be a "cold" compression test, but that's OK...

 

The 351c shares the small block bell pattern with the 302/351w. The 351m shares the big block pattern with the 400 and 429/460.

--Mike

 

I say forget the 351, M or otherwise. The 390 will be a much better engine IMO. Others have outlined the problems that swapping will cause. A little rust means nothing, a quick trip to the hot tank and all that will be gone.

I say rebuild the 390. It's probably just a gasket that let the water in. Tear it down and find out.

 

it looks like im going to rebuild the 390 it will just be less work thanks for all the input.