AutoAnything's Guide to Better Gas Mileage: Glossary
Air intake
The engine component responsible for providing air for combustion. A typical air intake comprises an air box, which contains the air filter, and an intake tube, which delivers the clean air to your combustion chamber.
Intake tube
In an air intake system, the intake tube connects the factory air box or performance filter to the mouth of the throttle body. Intake tube designs can vary greatly. Stock models typically feature a number of bends and a smaller tube size. These design characteristics of stock intake tubes help the intake system fit in the engine compartment and reduce intake noise.
Performance intake tubes look drastically different. The tube diameter is usually much larger than a stock part, and bends/turns in the tube's shape are minimized to improve airflow. Materials and particular design characteristics vary by model, as manufacturers do what they can to maximize performance.
Air/fuel ratio
The ratio of air to fuel used during the combustion cycle of your engine. Mixtures heavy on fuel are called “rich,” mixtures light in fuel are “lean.” Engines come with a pre-set programming of air to fuel ratios, known as a fuel map. Your engine senses the amount of air entering the combustion chamber and responds with the corresponding amount of fuel based on the correct ratio.
Mandrel bending
This type of bending is the least restrictive and will give you the most performance because the pipe's diameter remains the same throughout the bent areas. To keep a pipe's size uniform, a flexible rod called a mandrel is inserted inside the pipe before it is bent. With the mandrel inside, the pipe can be bent without crushing in on itself. This is critical, as a crushed pipe will diminish airflow.
Shift points
These pre-established points are married to a specific RPM threshold at which your automatic transmission throws to the next gear. Performance modules and programmers most often change these shift points to get you into high gear faster than factory settings, which are both more powerful and more efficient than lower gears.
Spark timing
Refers to the point at which the spark plugs fire to ignite the air/fuel ratio mix in the combustion chamber of your engine cylinders. Performance programmers modify this setting to fire when the piston head is closer or further from top dead center of the stroke.
Drag
Drag is the word for air resistance that slows down your vehicle while driving. The effect is more pronounced at higher speeds. Many methods are used to reduce drag. You've probably noticed the more curved, less upright shape of modern trucks, SUVs and cars — these are design changes meant to combat drag.
Though many parts of your truck contribute to drag, the main culprit is the tailgate, which acts as a large catch that snags passing air, slows you down and eats gas mileage. Pickup owners will drive with their tailgate down, replace their tailgate with a cargo net, or remove the tailgate altogether to reduce drag. Studies have show, however, that adding a tonneau cover is much more effective at improving gas mileage than these alternate methods.
Intake manifold
The engine component that distributes air into the individual cylinders for combustion. Airflow is fed past the throttle body and into the intake manifold by the air intake, specifically connecting to the intake tube.