These are the connections between the
cylinder head and the plenum area. They must flow
enough air at peak rpm to support the horsepower
your engine is capable of, but not be so big that they
have extremely low velocity at low rpm. The runner
length is also very important if the induction pressure
waves are to be used to increase volumetric
efficiency. Runner taper is also important to
consider (see the Tuned Port Section below) for
more info).