A rear facing scoop will blow hot engine air into toward you interior-air intake at the base of the windshield, making it hot and stinky inside. On the other hand, it will suck hot air out of the engine bay while running, drawing more air through the grill.

A forward-facing scoop will force cooler air into the engine bay while running.

Neither would do much at idle, I think.

I'm considering a small one on the front left corner of the hood to feed the air filter (if I go cone). I have to get the hood repainted, so why not do it then?