Rear facing NACA ducts

abn

I really don't know much about fluid dynamics and just recently started taking freshman math and science courses, I'm wondering if anyone here can help me with the following problem.

I am looking for an engine bay exhaust duct. I have a chassis catalog listing some fiberglass NACA duct inserts, the catalog states to reverse them for use as exhaust ducts...my question is: Is there any benefit or detriment to using a NACA duct as an exhaust duct? I gues they could help re-accelerate the engine bay air to outside airstream velocity...can anyone give me some insite into this or an easily accesible reference...I've been looking over the old NACA papers on the NASA site but can not find an instance of their use as an exhaust.