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Hafliger also milled the cylinder heads 0.050 inch to reach his goal of a 9.8:1 compression ratio. Unlike open-chamber big-block Chevy heads, these 906 castings (popular on 440 engines) have shallower, 86cc combustion chambers. Milling the heads brought the volume down to 79 cc. He replaced the original valves with Manley parts of the stock diameter (2.07-inch intake, 1.74-inch exhaust). He performed a standard, three-angle valve job and a 20-degree back cut on the intake valves before installing them.