This was taken from another FORUM
What is VICS?
VICS is "Variable Inertia Charging System" and is also refered to as "Variable Intake
Control System". In conventional intake manifolds, they are designed to have an air flow
compromise between low end and top end power. Because of this compromise, power
delivery from the engine is not optimum nor ideal. What some manufacturers (such as
Nissan and Mazda for example) have done is designed the intake manifold to have an
isolated runner system (there are many types of intake manifolds) to offer the best flow
characteristics. They didn't stop there. To squeeze as much power out of the engine, yet
allowing the vehicle to be streetable and mass producable, they added a secondary set
of intake runners into the manifold. With this dual runner system, there is the long runner
system for low to mid level RPM operation, and the short runner system for high RPMs.
On Mazda's dual runner intake systems (hereafter refered to as "VICS"), they designed
the long runners to be narrow and oval in shape to help promote air velocity at the lower
RPM ranges. As for the short runners, they are much larger and circular in shape to allow
for maximum flow capability at high RPM. There are butterfly shutter valves fitted over
the short runner and they are normally closed off. When engine speed is reached to a
predetermined rate by the ECU, a solenoid valve is opened and vacuum opens the
butterflies to allow for additional air flow into the engine. Hence the reason why the
system is "variable". It allows for optimum drivabilty and performance at most RPM
ranges. Note when this system is used with high boost forced induction systems, they
hinder performance rather than aid it because of the runner sizes. For high boost
applications, it is recommended that a large single (stage) isolated runner intake manifold
be used.
What is VTCS?
VTCS is "Variable Tumble Control System" or commonly refered to as swirl control
valves. This system only exists on the 3rd generation ULEV certified cars and is used
only on engine cold starts (under the following criteria: coolant temperature is less than
65C/149F). When active, the butterflies located at the end of the intake runners are
closed leaving a small notch aproximately 1/4 the size of the runners to allow for
turbulent air flow to reach the head and combustion chamber. The swirl caused by the
turbulent air aids the combustion process when the engine is still in its cold state "rich
fuel mixture" condition, therefore reducing cold start emissions. Hydrocarbon emissions
are significantly reduced due to this system. This system is also the cause of the infamous
cold start engine rattle that seem to happen between 2500-2800rpm on some 2.0l
engines. There is no known legal fix to this issue yet and Mazda is aware of the problem.
What is happening on the few 2.0l engines is normal and there is no need to worry. The
inclusion of this system also causes some performance restriction to the engine even when
the system is inactive.
