As prefilters for engine combustion air, pairs of Feifel aircleaners were mounted on the left and right upper corners of the hull rear ( Starting in November 1942, mounting plates had been installed on Chassis number 280014 in October 1942 but no filters were install until November ).
Air was drawn in through flexible ducts on the engine deck, passed through the prefilters, and then through flexible ducts to a slit cut into the engine harch, where it entered the engine compartment. Except in dust-free conditions, the round armor cover over the engine compartment airintake ventwas to be kept closed as long as the Feifels were in operation.
Feifel prefilters with a simplified upper chamber were introduced in March 1943. Feifel prefilters with the brackets for hoses and duct work on the engine deck were discontinued in October 1943. The airintake slit in the forward end of the engine hatch was then protected by an elevated plate. However, the small mounting plates were still welded onto the top of the hull rear into December 1943.
Brackets installed from number 250014, filters install from about number 250040,filters dicontinued from about number 250570-600, mounting plates discontinued from about number 250700.
You can read more in Thomas L. Jentz's book ; D.W. to Tiger I Design, production and modifications.
These informations are varified in Achtung panzer #6.