What does secondary air intake mean?

At present, there are many products made by using the principle of secondary air intake on the market, which are used by many people and are not cheap. It is called "secondary air intake" because besides the original air inhaled from the air cleaner, it also uses the vacuum pressure difference of the intake manifold to connect another air intake device from the PCV (Crankcase Forced Ventilation) pipeline of the engine, and introduces a proper amount of fresh air to achieve the purpose of improving volumetric efficiency. The most important power improvement effect obtained by secondary air intake is in the early stage (low speed), because when the throttle valve is fully opened and a large amount of air enters the vacuum degree, the amount of air that can be introduced by the secondary air intake device becomes negligible. The most important thing for the secondary air intake device is to maintain an "appropriate" air intake. At present, the difference of products on the market lies in the different methods of controlling air intake. If the air intake is too small, the effect will be poor, and if it is too large, the vacuum degree will be reduced, which will affect the auxiliary force of the brake vacuum booster (air tank) and make the braking force heavier. The so-called' appropriate amount' is the result of research and test by manufacturers. When the air intake system is greatly modified, the cooperation with the oil supply system must be considered. If only the air intake capacity is greatly enhanced, and the oil supply system cannot provide enough oil supply to match it, it is bound to fail to achieve the purpose of improving horsepower, because the engine needs an appropriate proportion of oil and gas, not just a lot of air. In addition, the noise problem must be considered in practice. In the past, when talking about noise, people usually only thought about the sound waves generated by the exhaust pipe, but ignored that air intake would also produce noise. You may not know that in an ITC car with a catalytic converter, the noise of the intake is almost greater than that of the exhaust. Therefore, if you are a' practical performance' car owner, changing a large-flow filter element may meet your needs. You may need to think twice about whether to change it up again.