Joe chose to feed the Motown block through Air Flow Research (AFR) aluminum cylinder heads. These particular heads are AFR's CNC-ported raised runner 215cc models. Joe says that these heads are really close to being perfect for the Challenge as-delivered, but he'll still give them the "once-over" to ensure all is up to his specifications. The heads will also run Ferrea stainless valves (2.08-inch intake, 1.6-inch exhaust), a brand chosen by AFR to ship with their cylinder heads. Joe appreciates the effort AFR has put into making the Ferrea design work well with their ports, and sees no reason to change valves.