Figure 3-15.Typical intake manifold.
walls and a minimum of bends that collect fuel to
reduce the condensing of the mixture. Smooth
flowing intake manifold passages also increase
Aid in the vaporization of the air-fuel mixture.
To do this, provide the intake manifold a
controlled system of heating. This system of
heating must heat the mixture enough to aid in
vaporizationwithout heating it to the point of
reducing volumetric efficiency.
The intake manifold on an L-head engine is bolted
to the block, whereas the overhead-valve engine has the
intake manifold bolted to the side of the cylinder head.
Intake manifolds can be designed to provide
optimum performance for a given speed range by
varying the length of the passages (fig. 3-16). The
inertia of the moving intake mixture causes it to bounce
back and forth in the intake manifold passage from the
end of one intake stroke to the beginning of the next
intake stroke. If the passage is the proper length so the
next intake stroke is just beginning as the mixture is
rebounding, the inertia of the mixture causes it to ram
itself into the cylinder. This increases the volumetric
efficiency of the engine in the designated speed range.
It should be noted that the ram manifold serves no
purpose outside its designated speed range.
As stated earlier, providing controlled heat for the
incoming mixture is very important for good
performance. The heating of the mixture may be
accomplished by doing one or both of the following:
Figure 3-16.Ram induction manifold.