gunpig0313

Ok I've been running my hood like this for 2.5 yrs no problems. The water that get in is very minimum, not enough to mess anything up. It's not like you taking a water hose to the engine @ 230 degrees. You will get some dirt in there if you live in a dirty area.

AirBrontosaurus

True, however when you open up the scoop you force a lot of air into the engine compartment when you're at high speeds. This raises the effective pressure in the compartment, and makes it harder for air to flow over the radiator. Also, since the airmass impacts at different directions and velocities, it creates all sorts of vortexes and other things that hinder good airflow.

Also, most aftermarket hoods don't have a giant hole in the top of them. Although the volume of the underhood area may change, the actual airflow remains pretty constant.

And if you're talking about aftermarket cowls: This is one reason why hood cowls face the driver instead of facing forward; they want more air to get into the engine bay, but if they simply rammed it in their it would create problems.

OP, it's your car, and you can do whatever you want. Some of the solutions here look pretty nice, such as drilling out the honeycomb but leaving the majority in there. However, most people who ask this question just want to rip all of the plastic out and have essentially a huge, gaping hole in the top of their hood.

Also, depending where you live and when you drive, you could very well get a decent mass of water into your engine bay. A light drizzle certainly wouldn't be a problem, but a downpour at 60 mph? That is a sizable volume of water being forced directly onto the engine.