Look at the optimum shift from the engine structure

We all know that the intake and exhaust engine condition and the importance of efficiency, many advanced engine design in this regard is also the brains, such as variable valve timing, variable valve stroke, variable intake manifold length no not in the intake and exhaust conditions to improve the speed range, allow the engine to run in different speed range in the best condition.
Ordinary economy cars, especially the low grade of the European Department of the United States Department of the sedan's engine, basically did not use these three "variable" technology, including the the above Speaking Passat 1.8 engine. Hereinafter from the valve timing, the length of the valve stroke and into the trachea of ​​these three structures to illustrate why the ordinary engine, the shifting speed should be in the vicinity of the maximum torque speed.
Valve timing
The valve timing refers to the opening of the intake and exhaust valve timing is controlled by the rotational angle of the camshaft. The the ordinary engine camshaft angle is fixed, so the valve timing is fixed.
We know, air is inertial, in the moment of the intake valve opening, air and not by the time difference quickly into the cylinder, he needs a very short reaction time, Therefore, in the design of the engine, it will enter the suction (that is, before the stroke of the piston is run down before), advance to open the intake valve, in order to offset the time difference of the intake air in order to obtain a more adequate intake air. In the exhaust stage, the same principle, when the exhaust gas rises to the top of the piston, the exhaust gas is not discharged to the maximum extent, due to the inertia and speed, exhaust emissions, the most amount of time appears to rise to the top of the piston after a very short time. In order to more fully in the exhaust gas, the need to make the exhaust gate delay moment then close after the piston reaches the vertex. This one in advance, a delay, there must be a period of time the intake valve and the exhaust valve is opened at the same time, this phenomenon is called "valve superimposed angle.
The engine at the time of high-speed and low-speed operation, the demand for superimposing angle is not the same. Smaller superimposed a large the superposition angle, high speed, low speed, angle - the angle of an overlay can be suitable for high and low speed. But the ordinary engine valve timing is constant, that is, the valve superimposed angle is fixed. For no special needs of the engine (such as racing engine will be intentionally designed to adapt to the high speed the smaller the superposition angle), valve superimposed angle design tend to take a compromise value, in this compromise speed region superimposed angle is the most appropriate. The most appropriate there is inappropriate, this fixed valve superimposed angle at low speed and high speed, the working state of the engine is not the best. This is not hard to understand why the low conversion file uncomfortable - did not get the best valve superimposed angle, the poor state of the engine work, torque and side effects. Before it comes to older drivers who may not know, he was driving like that all day, not only the power of small, very serious damage to the engine. Passat 1.8 engine is the design of the German superimposed angle of the engine is deliberately designed to be high-speed demand - because almost all of the German car like the high-speed transmission. Opposite the old master, so most of the time this poor high rpm engine to meet the high turn demand valve superimposed angle design at least it is not suitable for low rpm run, let it run low rpm is very unhealthy. It is also understandable why his Passat is always something wrong with it!

Valve stroke
The stroke of the valve is determined by the length of the camshaft corner, most of the engine's valve stroke are immutable.
The valve stroke determines for each valve in the intake cross-sectional area, this value in the high engine speed and low speed is the demand is not the same. When the engine in high speed, you need a relatively long stroke of the valve to the large intake cross-sectional area, thereby increasing the speed of the high speed intake, increase power output; When the engine is at low speed, shorter valve stroke, to produce a greater negative pressure.

With the intake valve opening and closing of the air intake manifold inside there will be an oscillation process. , The air inside the intake manifold when the engine air intake flow based on a constant speed to the cylinder in the intake valve closes instantaneously, the air flowing through the intake valve blocking, due to the characteristics of the movement of air, this part of the air to the accumulation of the direction of the intake valve (i.e., compression), and then in the opposite direction to rebound, and so forth, the formation of oscillation.