This! Plus, the only way to do properly is with heads removed and disassembled completely because porting involves machining or grinding for material removal and reshaping the ports, neither of which you can do without getting chips, and other abrasive materials into the valves, guides, seals, etc., which is obviously no bueno. That is not even mentioning getting into the intake tract, which should be obvious as not ideal. Then, there is the negligible gains without proper cams, compression, etc. to take advantage of the added flow...