No where near enough. Common and effectice practice with radial engine cowls and dummy engine cylinders is to cut away most of the dummy that is directly in front of the real cylinder.

Even more important is to let the air out at generally twice the area than the inlet. This is usaully positioned at the firewall on the underside.

Far two many nice scale planes have been lost because the owner would not let the engine compartment breath so the engine could be cooled.

John