Originally Posted by tuffss
why use 20-30 year old block some with helicoils, some already 060" over, when new improved blocks are readily available
Originally Posted by Miller Time
I just looked on the GM Performance website for the 454 Gen VI block, and it says it has a .060 max overbore, can that be?
'Cause the old blocks are stronger? 'Cause the old blocks have thicker cylinder walls?
I have heard, but not experienced, that the Gen 6 blocks are quite weak. I would expect about the same from the Gen 5. Probably not an issue at lower power levels, though.
NEW heads will bolt onto OLD (Mk IV) blocks without issue, provided you use a head gasket that matches the BLOCK. Mk IV heads can be a problem on Gen 5 blocks. Victor/Reinz makes a pair of special head gaskets to ease that problem, though. There is a different part number for the left and the right side.
The 2-piece neoprene seal works just fine. I think the REAL reason the factory changed to the one-piece seal was to make an easier/faster/cheaper installation, not so much as to "fix" an oil leak problem. Mind you, if it DOES leak, the one-piece seal is much simpler to change than the 2-piece.