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We started with our dismembered 489ci Rat (4.250-inch stroke, 0.030-over 454), which will debut in a couple of months. We mocked up the crank, camshaft, and one piston and rod along with a cylinder head. The key to accurate valve-to-piston clearance is to first degree the cam to ensure it is accurately phased. Any change to cam timing, either advancing or retarding, will affect valve-to-piston clearance.