An old time friend of mine was an engineer for GM. He explained that the single snorkel on most of the lower performance engines was designed for noise containment! The venturi designed into the snorkel allowed the air to enter, but was restrictive to the resonating sonic waves generated when the throttle blades were open. This trapped them inside the air cleaner, and contributed to a quieter engine bay. They were in no way restrictive for the smaller engines, and used only on the lower performance applications (even on the bigger engines) where quiet operation was expected by the customer.
