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With symmetrical heads, such as GM Gen III/IV castings, the prototype ports and combustion chamber are cloned for the remaining three cylinders. This ensures that every single port and chamber in the head is identical, a feat that's nearly impossible when porting by hand. The port on the left is a hand-ported port, while the others have been cloned using Verisurf software based on bore spacing of the block. The software is so precise that it allows modifying a hand-ported surface even further.