109 Block

[Chris Brooks]

Built up a 109 short block for my hot air. Wondering if I should change to the 87 head gasket or stick with the 85.

 

[6SENSE]

Im guessing the '87 gasket, because they are thicker than the the '84s to go with the shorter deck height of the newer block. From what I hear the thickness of the'87 gaskets compressed is .060 and the '84's is .018. There is a thread over in the General Tech forum titled Head Gaskets (I think), might have some more info.
Im sure someone else that knows for sure will chime in, but I am willing to bet the '87 gaskets are the way to go to give you the correct compression ratio.

P.S. on my engine, the compression ratio went up slightly with .030 over bore, but went down by putting '87 gaskets on it.

 

[FJM568]

Using the 109 block, if you want to keep the factory compression ratio, you need to use the 86/7 composite head gasket...Either the stock ones from GM or the 9441's from FelPro...

Did you have the block bored??? If you went +.030, I think the compression jump from the increased bore alone is like .25 a point...If you just use 1 steel shim 84/5 head gasket per side, then you can add about another .25 to .50 a point...

Hope this helps...