The Air Filter Housing
Most aftermarket air intakes do not have air intake housings.  They are an air filter attached to a “heat shield” and a plastic air intake tube.  While these “open element” style intakes test well on a flow bench, they have two major flaws.

First, an open element air intake does not protect your engine from dirt and debris.  When you clean your engine compartment notice how much dirt accumulates there.  Without a sealed air box all this dirt is hitting your air filter and potentially entering your engine.

Second, an open element air intake is not sealed so it sits in the engine compartment ingesting hot engine air.  Hot air robs a vehicle of horsepower and fuel efficiency.  Fuel combines with oxygen to combust in your engine’s cylinders.  Hot air contains fewer oxygen molecules than cold air.  The colder the air, the more efficient your engine is.  The air filter is sitting in the engine compartment with a useless heat shield.