It shouldn't pull air out because of the suction of the engine. I louvered the well liners behind the intercoolers in my Z to create a low-pressure zone to extract air, but there was no opposing suction and the direction of flow was outward anyhow. Your engine is actively drawing air inward and that will more than compensate for any pressure-gradiebt-driven airflow out of the box. With the engine running air will draw inward. Even if some air enters the box from the grille scoop and goes right down, you'll still get all the air you need for combustion and you'll still increase the sound of the turbo which was your stated purpose for the mod. You'll be fine.

 

Cool, thanks.

Any idea about the flapper?

 

Bump.