A intake valve open when the piston reaches the top of the cylinder and just after the exhaust valve closes. It allow fuel and air to enter the engine cylinder.
As an air/fuel mixture is drawn into the intake ports, intake valves open to allow the mixture to enter the cylinder. On the exhaust stroke of an engine, the exhaust valves open, allowing the burned air/fuel mixture to exit out the exhaust ports. Intake valves are larger than exhaust valves, and are able to be found on the "cold" or intake side of the cylinder head(s).
Trick Question! ...depends on the RPM the engine is running at.
There is a short time between the exhaust and intake stroke where all the valves are slightly open at the same time. This period of time is called valve overlap. This is because the intake valves are just starting to open as the exhaust valves are just finishing closing. This is done so flow through the engine can be maintained at engine operating speeds.
The valves in a car engine are opened and closed by a cam shaft driven by the engine crankshaft. they allow the flow of gases and fuel into the engine and the burnt gases out of the engine into the exhaust system.
-intake: exhaust closed, intake open -compression: exhaust closed, intake closed -combustion: exhaust closed, intake closed -exhaust: exhaust open, intake closed
overlap
There are two types of valves in an engine. The valves are located in the head. There are exhaust valves and fuel intake valves
The intake valves are in the intake ports, the exhaust valves are in the exhaust ports.
To open/close the intake/exhaust valves.
To open/close the intake/exhaust valves.
The intake valves can hit the exhaust valves.
The intake runner control is in he intake manifold. It consists of a shaft and 3 butterfly valves for each cylinder bank. The opening of these valves are controlled by an electronic module located on the back of the engine behind the intake manifold ducting on top of the engine. Each set of butterfly valves are connected to the module by a link. When the computer notifies the module to open the butterfly valves, it rotates a small motor in the module, moves the links and opens the butterfly valves. The module is very difficult to get to and you must remove the top ducting to see the links and the butterfly valves