I would like to build a 425. I know that there are 2 different tappet bank angles and different diameter tappets. The 39 degree .921 dia. block was the hot ticket of the day, but the major components in both engines were the same. What is the down side of using a 45 degree .842 dia. block as the basis of a performance build? 2cd. Question; Max bore on 400 V/S 425?

 

Just because it has .842 lifters doesn't mean it is a 45º block. All 1967 425 engines I have/have seen were 39º engines. The 1965 & 1966 425 small lifters were 45º. The cam 45º cores are getting harder to find but you can get them. Comp Cam was out but check anyway. The 425's are excellent engines to build either cam bank angle. Jmo, Ken

 

if you want to be sure about what you have, check the lifter bank angle for yourself. my '67 425 is a 45* lba with .842 lifters.


bill

 

X2.

If you want to go roller then the 39deg/.921 lifter block would be the most practical.
You can get roller cores for the 45 degree stuff but they're twice the cost of the 39's.
All you need to use a roller in a .921 block is the spider and dog bones from a diesel or roller 307. Then you're good to go.
I'd go with the 425 block with the bigger bore but it's always a good idea to have them checked anyway.