Yes, the flap is to allow for proper performance, despite the otherwise single-snorkel construction of the air cleaner. Looks like enough space to allow for the necessary air, too. Any air is better than no air, but air from outside the engine compartment is always best. On my first Barracuda, I used a 4" dryer duct for the fresh air hose to the air cleaner snorkel, and routed it to the rad support, under the battery tray. Instant horsepower increase, better fuel economy, and I used a grand total of about $.25 of duct tape. Everything else was just lying around.
