E46 M3 Hood Vents - Large
Heat under the hood/bonnet can be significant and increases with revs & load. This energy convecting into the air and radiating off the manifold and block makes the engine bay a literal oven. This heat is absorbed by nearby components with the only means of escape being air flow down the narrow and turbulent transmission tunnel.
Releasing this heat through the hood of a car is a great way to reduce engine bay temps, reduce front lift and promote airflow through the radiator for more efficient cooling.
The CMP hood vents are installed from beneath with either rivets or epoxy and designed specially for the E46 chassis to maintain under bonnet airflow where it is needed then expel it directly above the exhaust manifold to promote natural convection at a stand still. The effectiveness of these vents increase with speed as the gurney flap increases the pressure differential to pull the hot air out.
Installation is as simple as lining up the unfolded vent tabs against the bonnet bracing to take the guess work out of getting the correct position and angle followed by drilling some holes and connecting the dots with a rotary tool before bending to the desired angle of attack and painting.