See if this helps. Here’s the static compression ratio for a stock 312 and assuming a zero deck. This is using fibre or composition head gaskets and not the original steel shim head gaskets. If the pistons are sitting 0.028” in the hole, then reduce the compression ratio by another half a point.
6.252 | Rod Length |
3.800 | Bore |
3.440 | Stroke |
69.0 | Head cc's |
0.000 | Deck Clearance (in.) |
10.00 | Head gasket cc's |
312.11 | Cubic inches |
9.09 | Static compression ratio |
And here’s the static compression ratio for a 312 bored +060 over (same zero deck) with the heads milled 0.010”. This is assuming the heads were 69cc to begin with
6.252 | Rod Length |
3.860 | Bore |
3.440 | Stroke |
67.4 | Head cc's |
| |
0.000 | Deck Clearance (in.) |
10.00 | Head gasket cc's |
322.04 | Cubic inches |
9.52 | Static compression ratio |