Many people don't realize that the cylinder bore is equally important to the airflow of the cylinder head, and that the airflow doesn't stop when the last bit of air leaves the combustion chamber. If the chambers need to be unshrouded because of larger valves or just for poor chamber design, most times the cylinder bores also need to be notched to further enhance and help the head flow to its fullest potential. A cylinder head won't flow 260 CFM,(if it flows that on a flowbench), if the cylinder bore shrouds the valves.
Flowing a cylinder head on a fixture that correctly locates the cylinder head relative to that engines bore/chamber location is important in that regard, or it just leads you to incorrect conclusions as to its abilities.
Winston Cup teams still flow test all of their cylinder heads in a final evaluation with the heads bolted and torqued onto the actual engine block the heads will be raced on so they can get as accurate of a account of how it will flow in the environment it will be used in.
