Whether gas or diesel, the power principle remains the same: More air in and more air out equals improved horsepower and torque. In order to understand this philosophy, you have to get down to basics.
First and foremost, an engine, whether gas or diesel, is essentially a giant air pump. The up and down motion of the pistons moves specific volumes of air though the engine. The quantity of air depends on a lot of factors: the displacement of the engine, the size of the intake system, the camshaft configuration, and the efficiency of the powerplant's exhaust side.
1. AIRAID's intake system...
1. AIRAID's intake system for the '03-'05 Ford Power Stroke V-8 diesel is a complete replacement setup that uses the factory air inlet location and has provisions for the OEM mass air meter.
On a typical four-cylinder engine, the atomized fuel mixture is drawn into the cylinder and past the open intake valve by the piston's downward motion. As the piston moves upward, the air/fuel mixture is compressed and ignited. The force of the explosion pushes the piston downward. This is called the power stroke. On the piston's return upward, the burnt gases are pushed out through the open exhaust valve, and the process repeats.
By improving the efficiency of the engine in any one of the critical areas, such as intake, valve timing (camshaft), ignition, exhaust, you can produce more power. Most manufacturers face quite a challenge when it comes to designing intake systems for today's trucks. First off, they have to fit the platform (model) they are for. Second, they have to thoroughly filter air coming into the engine, and third, in order to reduce the vehicle's overall NHV (noise, harshness, and vibration), they have to be somewhat quiet. What's left is what you get on your new truck. Does it work? Yes. Is there room for improvement? Definitely.
2. The stock air intake system...
2. The stock air intake system uses a large filter that sits inside a plastic housing on the driver side of the engine bay.
On a stock air-intake system, the main airflow restrictions are caused by the intake box's design itself: the actual air inlet where the box meets either the inner fender or the radiator bulkhead, and the factory, paper-style filter inside the box.
The easiest upgrade to any intake system is to simply change the filter from a paper-style element to a high-flow-style filter. The most common performance air filter is an oiled, cotton-gauze style that flows more air dirty than the stock paper-style flows clean. Filter specialist AIRAID has taken the standard cotton-gauze filter to the next level by adding a synthetic layer of filter material that improves filtration (down to 2 microns) without affecting airflow. The company's SynthaFlow layer is now standard on AIRAID's line of direct replacement filters as well as all of its intake system filters.
 3. We began the install by...  3. We began the install by removing the stock filter element. |  4. With the element housing...  4. With the element housing removed and hoses disconnected, the front half of the factory intake was pulled from the radiator core support. |  5. Next, the wires connected...  5. Next, the wires connected to the factory mass air meter were unplugged. |