How to adjust the secondary air intake of hks to achieve the best effect?
I. volumetric efficiency
When the engine is running, the amount of air that can be obtained per cycle is the basic factor that determines the power of the engine, and the intake capacity of the engine is measured by the' volumetric efficiency' and' inflation efficiency' of the engine. The definition of "volumetric efficiency" is the ratio of the air volume inhaled by the cylinder at atmospheric pressure to the stroke volume of the cylinder piston in each intake stroke. The reason why it should be used as a standard is because when air enters the cylinder, the pressure in the cylinder is lower than the external atmospheric pressure, and the pressure value will change, so the volume at one atmospheric pressure is used as the standard of * * *. Moreover, due to the intake resistance and the high temperature in the cylinder during the intake stroke, the volume of air sucked into the cylinder must be smaller than that converted into atmospheric pressure, that is to say, the volumetric efficiency of naturally aspirated engine must be less than 1. The decrease of intake resistance, the increase of cylinder pressure, the decrease of temperature, the decrease of exhaust back pressure and the increase of intake valve area can all improve the charging efficiency of the engine, but when the engine runs at high speed, the charging efficiency will decrease.
Second, the filling efficiency
Because the density of air varies with the atmospheric state (temperature, pressure) at the inlet of the intake system, the volumetric efficiency cannot represent the actual air quality entering the cylinder, and must be explained by "filling efficiency". The definition of "inflation efficiency" is the ratio of the air mass inhaled in each intake stroke to the dry air mass in the standard state (1 atmospheric pressure, 20℃, density: 1. 187Kg/㎡). When the atmospheric pressure is high, the temperature is low and the density is high, the filling efficiency of the engine will also be improved. It can also be seen that volumetric efficiency represents the difference of engine performance caused by engine structure and working state, while filling efficiency represents the change of engine performance caused by atmospheric state at work.
Intake manifold and volumetric efficiency
Another important factor affecting volumetric efficiency is the length of intake manifold, which will also lead to two effects related to volumetric efficiency: pulsation and inertia.
First, the pulsation effect
Unless the engine speed is extremely low, the pressure in front of the intake valve will change continuously during intake. This is because the opening and closing actions of the intake valve make the compression wave in the intake manifold fluctuate back and forth at the speed of sound. If the length of the intake manifold is designed correctly, so that the compression wave can reach the intake valve at an appropriate time, the oil and gas can enter the cylinder by its own fluctuation, which will improve the charging efficiency of the engine, otherwise it will lead to a decrease in the charging efficiency. This phenomenon is called the pulsation effect of intake manifold, and it is also called "* * * earthquake effect".
Second, the inertia effect.
When the steam inlet valve is opened and air flows into the cylinder, even if the piston has reached the bottom dead center, air will continue to flow into the cylinder. If the inlet valve is closed when the pressure in the cylinder reaches the maximum, the volumetric efficiency will reach the maximum, which is the so-called inertia effect. In order to obtain the best volumetric efficiency, the pulse effect and inertia effect must be tested at the same time, that is, when the cylinder pressure reaches the maximum and the intake valve is closed, the compression wave in the intake manifold also reaches the highest position (peak). The longer intake manifold has higher charging efficiency and higher maximum torque at low engine speed, but with the increase of engine speed, the charging efficiency and torque will drop sharply, which is not conducive to high-speed operation. Shorter intake manifold can improve the charging efficiency of the engine at high speed, but it will reduce the maximum torque of the engine and its appearance time. Therefore, in order to give consideration to the high and low speed power output of the engine and maintain the volumetric efficiency at any speed, the variable length intake manifold can only be used.
Modification of air intake system
The improvement of the intake system is based on improving the "volumetric efficiency" of the engine. In order to achieve this goal, we can usually start from the following aspects:
I. Air filter
The entry work of air intake system modification is to change an air filter with high efficiency and high flow. Common brands on the market are K &；; North, HKS, arc, etc. Replacing the high-flow air filter can reduce the intake resistance of the engine and improve the intake volume and volumetric efficiency per unit time when the engine is running. The increase of air intake is measured by the air flow in the fuel supply system, and the signal is sent to the fuel supply computer (ECU), which will control the fuel injector to spray more gasoline to cooperate with it, so that more oil and gas (not rich) can enter the cylinder, so as to increase the horsepower output. If the filter element can't meet your needs, you can replace the whole air filter with an exposed filter element, commonly known as "mushroom head", to further reduce the air intake blockage and enhance the "vital capacity" of the engine. At present, the most famous one on the market is POWER FLOW of HKS.
Second, the air inlet.
The modification of inlet can be divided into two aspects: shape and material. The purpose of changing the shape of the intake port is to store the intake pressure (used for sudden opening of the throttle during rapid acceleration) and increase the intake flow. However, this kind of products usually have special restrictions, that is to say, if they are installed on B-type vehicles, they may not be able to exert the greatest effect. For example, the' fat sausage' that was popular a while ago, its appearance is copied from the car of Mugen Factory, which is dedicated to Messi, but it will be effective if it is installed in other cars. Change the inlet material, the key point is not to absorb heat and light weight. The most commonly used material at present is carbon fiber. Its non-endothermic characteristics can make the intake temperature completely unaffected by the high temperature of the engine room, and make the intake density higher, that is, increase the oxygen content per unit volume and improve the engine output power. The only drawback is that the price is too high. The shape and material of the air inlet are often changed at the same time to achieve the maximum effect. At the same time, remove the air filter together, extend the air inlet to the outside of the car and aim it directly at the front, so as to increase the intake pressure and increase the intake volume with the increase of vehicle speed.
Three. Direct injection manifold
What racing engines need is high-speed power performance, and horsepower output can be sacrificed at low speed. Therefore, shorten the intake manifold as much as possible, cancel the air filter, fully eliminate the intake resistance, and achieve the best high-speed performance. The biggest problem faced by the traditional LIFO engine is how to introduce enough fresh air from outside the vehicle after replacing the direct injection intake manifold. Direct injection intake manifold and aerodynamically designed carbon fiber intake are the best combination, and also the best choice for racing factories and cars at present. Especially after the engine is lowered, a large air inlet is installed in the space above the engine, and the opening is completely sealed with the hood of the front water tank, which can effectively transport air to the rear intake manifold. At present, the factory car directly reverses the cylinder head, so that the intake manifold is directly aimed at the front of the car, and the intake becomes more direct.
Fourth, secondary air intake
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.