[Funny]

It's difficult to make a sand cast head with intricate details like these grooves in it, and labor to make each groove by hand before installation isn't justified by the ability to charge for the "Now with Singh-grooves!" head. That's my theory. Think how aerodynamically dirty stock intakes/heads/exhausts are, and then how much "cleaner" aftermarket units are. That sums it up. Cost to benefit ratio is too small.