# What is a high angle camshaft?
First, let me talk about what a camshaft is.
The camshaft is an important component that pushes the valve to perform intake and exhaust operations driven by the output shaft of the crankshaft. Each time the crankshaft of a four-stroke engine rotates 720 degrees, the four-stroke cycle of intake, compression, combustion, and exhaust is completed. The camshaft Driven by the crankshaft, the opening and closing of the valve is accurately completed. This process is the valve timing.
High-angle camshaft, also called High CAM, is relative to the cam working angle of about 240° of ordinary camshaft, the cam working angle of high-angle camshaft can usually reach more than 280°.
The design of the convex part on the high-angle camshaft is different from that of the original factory. Its working angle and head have been increased. The valve can only complete an opening and closing process after 280 degrees of rotation. The opening time of the valve is compared with the original factory. Has increased.
The modification of high-angle camshafts is mainly for naturally aspirated engines.
The increase in valve opening time and stroke means an increase in engine intake and exhaust efficiency, and an increase in intake means an increase in engine horsepower.
This is a design for a high-revving engine. Only when the engine is working at a high-revving speed, dongfeng truck its power can be fully utilized. The violent speed-up feeling can only be experienced by those who have used it.
# The working principle of high angle camshaft
First define a concept called "inflation efficiency".
To put it simply, it's like drinking a drink with a straw. When "cow drink", you must be eager to insert a thick straw milk tea special straw into the drink cup to take a sip, which is like the situation of the engine at high speed and full load.
But if you have to drink slowly for some reason, a straw with a smaller diameter will suck more efficiently. This is like the low-speed and low-load situation that we usually use when dfsk glory 560 driving.
Only when the piston moves fast enough, the greater the valve opening, the longer the opening time, will there be a higher suction efficiency.
Because the suction efficiency is determined by the air pressure difference between the intake port and the cylinder, if the inflation is too fast, the air pressure difference will shrink faster and the air flow rate will slow down.
# Why the racing engine idling speed is high
Valve opening is large for a long time. At this time, when the intake and exhaust valves overlap open, the exhaust gas backflow into the intake port will be aggravated. The residual amount of exhaust gas in the cylinder during compression will be too high, and the engine will run unstable at low speed.
One of the reasons for the high idling speed of the racing engine is that the crank connecting rod system and the flywheel of the racing engine are extremely light, with small rotational inertia, and can only maintain a stable speed when it is rotating at a high speed.
The second reason for the high idling speed of the racing engine is that the speed of the racing engine is generally high. When using high-angle camshaft technology, the valve opening is large for a long time. At this time, when the intake and exhaust valves are opened overlappingly, the exhaust gas flows back into the intake port. The situation will be exacerbated, and the residual amount of exhaust gas in the cylinder during compression will be too high, and the engine will run unstable at low speeds.
# Replacement of high-angle camshaft for self-priming engine
For self-priming engines, in addition to intake and exhaust, replacing the camshaft that is more conducive to intake and exhaust is a good choice to increase power.
Better ventilation brings higher VE, that is, better horsepower and high speed performance.
If you want to extend the maximum speed, it is best to replace the camshaft and intake and exhaust together.
The main disadvantages of changing camshafts are: the idle speed needs to be increased, and the power performance at low speeds will be lost. So just for the pursuit of high-speed power, some high-angle camshafts that are heavily used in racing are not suitable for usual street driving.
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