Are the Stage II 3.8 & 4.1 blocks the same, with just different bore sizes?

Awesome T

New Member
Jan 25, 2002
Are these blocks all siamesed, or are there water passages in a 3.8 and not in a 4.1 block? How far can a stage II 3.8 block be safely overbored and still keep good cylinder thickness (>.200)? Thanks. John.
4.1's are siamesed, almost all 3.8's are not. (A very few blocks marked 3.8 were siamesed.) Overbore depends on cylinder wall thickness in each block, but if you're thinking of overboring a 3.8 for a big increase in displacement, look elsewhere.
Thanks Mac

How far can a Stage II 3.8 siamese be taken out to? I know some manufacturers have built the same block with different bores to make certain displacements, and am wondering if this would be the case with siamese 3.8 and 4.1 blocks? John
The one thing that is almost certain about stage 2 blocks is they are all different. I've owned 9 different Stage blocks and no 2 were the same. Buick made casting changes on the fly during the development and production of these blocks.

So if one person tells you something, it may not apply to all other Stage blocks.

If you want to bore a 3.8 S2 block to a big dimension, you best have it sonic checked first.
Turbodave is exactly correct. I have seen 3.8 blocks that were 3.8 + .060
only, and I have seen 3.8 blocks that were good for 4.100 bore. Please take the time and effort to haVE IT SONIC CHECKED before you make a bad decesion. Mike:cool:
Thanks guys.

It was great that Buick catered to the racers and built essentially custom, small-batch pieces for them when needed. I appreciate the help.

Also, I'm in the market for a SII. Please email John.
John, I have some that may work for you. 937 272-4313 Mike:cool:
I am in Dayton, Ohio