Crossbolted 390 block?

[Kerry j]

Just wondering what you guys think a crossbolted 390 block is worth. The sonic map looks OK for +.040 over but that's about it to be safe. Thinking of building a 4.25 stroke motor for my 74 F100 4X4. Are the crossbolts just a waste of money?

[e philpott]

not sure what a .040 over block is worth , but I think cross bolt mains would be a good edition to a healthy 445 ..... I have a 416 cross bolted with 1/2 fill and another block getting cross bolted for a healthy 445 in the future

[jayb]

FWIW, my rule of thumb is 600+ HP requires crossbolts, and below 600 HP doesn't.  This is somewhat arbitrary, but if you're going to put the money into an engine to make upwards of 600 HP, I think you ought to spend a little more to crossbolt the block.  Of course, crossbolts can't hurt, no matter what the HP level.