I have a 1970 f100 with a 390 and 4 speed i'm trying to decide if i should keep the 390 or swap it to a 351 or 302. was wondering if it would be worth the work or not.

 

Keep the 390. Much stronger engine.

 

X2 on the 390

 

really the only reason that i wanted to do the swap was so that i could get a little better mpg

 

You won't get any better mileage. Just keep your foot out of it.

 

The 390 is an excellent motor that was made for trucks very well and it has pretty good aftermarket support because it was used for quite awhile. Ford dint really ever call engines big or small blocks. They did use 2 bell housings. There is the 351m and 351c that are very simular blocks but the 351c uses the small displacement bell housing and the 351m uses the large. Ford even made a 400m in extremely small numbers that used the small displacement bell. If ya ever run across a 400m small bell it is very collectable...

 

Your tranny wouldn't bolt to a 302 or 351 anyway - the 390 uses the FE bolt pattern, the 302/351 uses the Windsor bolt pattern. The so-called "big block" pattern that the 351m and most 400's use is actually the 335 bolt pattern.

 

390 and a ring and pinion that will keep the rpms down while cruising.

 

I had forgotten/didnt know Fe motors had a unique bell.. I know the 351m/400m share the same pattern for sure with the 429/460 and the 351c is a 335 and it shares the bell pattern with the windsor 302 & 351

 

The 351c does not use the 335 pattern.

 

You should give the 390 to me.

 

I think i will keep it.

 

Old 390s run forever. They use some gas, but not as much as the 360s. The only reason I would replace a 390 would be to go with a 428 or 427.

 

I agree with keeping the 390. You would miss the power loss, regardless.

 

well i wouldn't know what kind of power it has because i just got it running yesterday.