.. The only ported vacuum I've ever heard of is a ported vacuum outlet on the carb. to block vacuum to the distributor vacuum advance when idling and allow that vacuum at part throttle cruising for better MPG...

.. Some vehicles also have a vacuum valve on the engine water outlet that in extreme cold winter weather/cold engine supplies vacuum to an air door vacuum motor in the inlet of the air cleaner to pull warm air off the exhaust manifold stove to prevent freezing up the condensation in the carburetor/freezing the carburetor(which is no fun)... you don't want that hot air going into the carb. most of the time...

.. There is also the EGR (ExhaustGasRecirculation) system anti-pollution control system that opens a valve that is usually in the intake manifold to allow hot exhaust air in the intake manifold to enter the engine at times...

.. Having positive deck pistons shouldn't be causing you detonation, should actually be lessening it... assuming you have head gasket that provides .030" - .040" quench distance, max ignition advance of 34-38 degrees, and gas of sufficient octane... like 91-94 octane pump gas plus an ounce or two of kerosene per tankful...