Completed drill and deburring for the firewall exit fairing. The deburring of the stainless on the cabin side of the firewall was done with a sandstone grinding stone.
To demonstrate the Coanda effect, I taped a plastic strip to the fairing, then gently blew on the fairing with an air gun. You can see the strip wrap itself around the fairing as it followed the airflow. This helps to direct and accelerate the high pressure heated air in the cowling, which improves cooling airflow and directs the airflow aft, adding a bit of thrust.