About this detail of the Tiger
The air vent in the Tiger's firewall was altered when the vehicle's engine was changed from the HL 210 to the HL 230 in May 1943  on hull #250251.
The reason for the change was on the engine itself. The HL 230 had a small gearbox at the top rear to drive its cooling fans. During underwater travel, the fans were flooded and had to be decoupled from the engine. To decouple them, you had to pull a "cooling gear handle" at the front of the engine. This handle is indicated by an arrow in the photo  above.
The crew needed access to this new handle through a door in the firewall. But the location for the door was already occupied by the air vent.
We don't have documentation about the new design, but a surviving German drawing  tells us, in part, how to upgrade old tanks with the new engine. These instructions are at the side of the drawing:
"c) The old air vent in the firewall is to be removed and replaced by a new vent that has a door. Before installing the new vent, 2 air holes in the firewall are to be combined by cutting out the crossbar. The guides for the vent remain unchanged."
And written on the drawing itself, beside the air vents, is:
"c) cut out the crossbar"
Combining the two air holes as directed, would give you the vent drawn above. But what lay behind these holes?
This is a German photograph  of the new vent in a tank manufactured around June or July 1943. The sliding panel here incorporates a hinged spring-loaded door.
This tank must have been built with a HL230, suggesting that this is the new design for the panel and that it was made upwards-compatible with older tanks.
To support this assumption, the Sturmtiger in Kubinka museum has a very similar sliding panel. The lever can still move the panel, though now it uncovers only 3 holes.
This detail from a German drawing  shows the "size of the open door" behind the firewall. We are looking to the right. The door is compared to the water pipes (both old and new) that connect to the front of the cylinder head block.(The latest version of this article)