These do work. When located on the forward portion of the hood, they can extract a substantial amount of motor bay air, at speed. The faster you go, the more air removed. Venturi design is the principle behind it. As well, the static pressure on the front hood is very low. The pressure under the hood is very high (especially with fan running). Air goes from "high" to "low"JJs CAT said:Rear facing extractor vents may be a very good idea for improving -P under the hood.
You just have to be sure that this air is not coming into the bay area via an alternate route, like the crack between hood and grill.
I have some small carbon fiber vents for someone to try. Getting you to cut the hood, that's another challenge.:bling: