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The R07 has noticeably more material on the top of the head. This adds approximately 5 pounds to each of the heads versus the SB2.2. Nobody likes extra weight, but the added material should provide a large amount of additional stiffness for the rockers, which can potentially make more power. The grooves aid oil drain, but they also direct oil to the intake valvesprings, which are higher in the head and will see less oil than the exhaust springs.