The purpose of the extraction vent is to increase the available airflow to the cockpit. The ASW-19 has NACA vents under the wing roots to draw air in, but there is no clear path for it to exit. The extraction vent, and modification of the bulkhead to allow airflow, gives the air someplace to go and reportedly greatly increases the comfort level in the cockpit. Noise reduction is primarily due to being able to keep the canopy vent closed and a reduction of "pressurized" air leaking under the canopy seals.

Any performance benefits are a bonus in my book and not a serious consideration unless you are a hard-core performance tweaker looking for every .1% gain.

Paul A.