Block casting #25500012

[6banger]

Is there and difference between these stage I and stage II blocks other than the stage I having provisions for the additional head studs,and provisions for 4 bolt mains on 2+3 ,I also know about the oiling system. I guess I`m asking are they both out of the same mold, with the same composition, just that the stage II has more machining done to it? So in essence, by drilling and tapping the heads and adding the 4 bolt main caps you can convert a stage I into a stage II?
Any advantages or disadvantages in converting a stageI to a stage II? And how large can you bore the cylinders safely?
TIA,
Jim

[turbodave231]

The stage 1 blocks were the identical casting as the stage 2 (offcenter blocks). Stage 1 blocks were machined just like the production blocks. They received cast main caps with bolts.

I have owned 2 of the S1 4.1 blocks and 2 of the S2 4.1 blocks. The raw castings are identical. You can machine a S1 block to accept 4 bolt caps on 2 & 3 but I have never talked to anybody who did this. This would take alot of setup to get the cap registers right on, and you would have to find the 4 bolt caps.

I talked to Dan Strezo at PTE and Ohio George and both these guys talked me out of converting a S1 block to S2 caps. Both recommended installing steel 2 bolt caps on all 4 positions. And that is what I did. This allows using a production oil pickup, dipstick and oil pan if you want.

#2 main cap outside bolt on pass side would be very close to the internal oil pump pickup passage that would be partiallly machined away. This area would be solid on a S2 block.

Downsides to the S1 block are: No priority main oiling, no solid roller lifters. Not as strong as a S2 bottom end, but much stronger than a stock bottom end.