Aug 5 In internal combustion engines, a variable-length intake manifold VLIM ,variable intake manifold VIM , or variable intake system VIS is an automobile internal combustion engine manifold technology. An intake manifold tuning IMT valve is used to change the intake manifold plenum configuration.
When the IMT valve is open, the intake manifold is configured to one large plenum. The variable intake manifold actuator VIMA controls the positions of the internal flaps and valves on the intake manifold runners to alter the amount and speed of air induction.
The image above shows a variable length intake manifold from a Honda application, in which the blue arrows represent the airflow through the manifold at different engine speeds. Note that depending on the engine speed, the length of the flow path of the intake air either increases or decreases, which is analogous to the manner in which an artificial restriction runner control flaps increases or decreases the flow rate of the intake air.
Note however, that in this example, the intake air can only follow a short, or a long path- there is no intermediate path to accommodate mid-range engine speeds. Variable length intake manifolds have now largely replaced intake manifold runner control flaps, but as with all automotive technologies, design specifics vary, as do the names manufacturers give to their version of what is essentially the same technology.
Despite their increased efficiency however, variable length intake manifolds are just as prone to failure as runner control flap systems are. Some common failures include-. The flap, or vane that switches the airflow between long and short flow paths has become known as DISA valves, although it should properly only apply to BMW applications.
Nonetheless, failure of these valves is a relatively common problem that causes a sound much like a sticky valve lifter when it starts spinning around its pivot point. On many applications, this valve can be replaced by partially disassembling the manifold. TIP: To ensure proper operation of the replacement DISA valve, ensure that all vacuum and electrical connections are sound, and that all stored fault codes are cleared before the vehicle is returned to service.
Position switch failure is common, and most failures can be attributed to heat exposure over long periods, vibration, and the build-up of carbon on the DISA valve that can inhibit the free movement of the valve. However, in many cases where codes relating to the position switch are set and stored, the real problem is not actually the position switch, but rather the inhibited movement or outright failure of the DISA valve.
As with all vacuum actuators, the diaphragm can become brittle, which causes it to fail. Like all automotive technologies, intake manifolds will continue to evolve to keep pace with developments in other aspects of fuel and engine management systems. In fact, Ferrari has managed to develop a variable intake manifold in which the runners physically change their lengths as parts of the runners telescope in and out of each other.
However, how successful this design will prove to be under real-world driving conditions remains to be seen. Toggle navigation Navigation. In this article, we will briefly discuss the importance of intake manifold design, as well as the various means and strategies engine designers have adopted to increase the efficiency of intake manifolds, starting with this question- What is an intake runner?
Which brings us to the role runner length plays in manifold design by asking this question- Why is runner length important? Let us look at this process in some more detail- As, say, piston number one moves downward on its intake stroke while the intake valve is open, the volume of the intake manifold increases by virtue of the fact that cylinder number one is now connected to the manifold through the open intake valve s.
If you need to top it off, be sure to park the car and let it cool off before opening the reservoir cap. Replacing a manifold gasket can be a daunting job, especially because of the danger of making a small mistake that can ruin your engine. Page Contents.
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