manifold is designed to prevent collecting of fuel at the
bends in the manifold.
iron castings or may be cast in sections. They have a
smooth interior surface with no abrupt changes in size.
The intake manifold should be as short and straight
(See figure 3-23.)
between the carburetor and cylinders. To assist in
Exhaust manifolds on today's automobiles are
vaporization of fuel, some intake manifolds are
constantly changing in design to allow the use of
constructed so that part of their surfaces can be heated
various types of emission controls. The most common
by hot exhaust gases.
type is the large diameter exhaust manifold, which is
designed for use with the air injection system.
Intake manifolds on today's gasoline engines have
special passages for allowing exhaust gases to re-enter
the engine. These intake manifolds are used on engines
equipped with an exhaust gas recirculation system.
The intake manifold on a gasoline engine carries
the fuel-air mixture from the carburetor and distributes
it as evenly as possible to the cylinders. On a diesel
engine, the manifold carries only air to the cylinders.
The principal stationary parts on an engine have
The intake manifold is attached to the block on L-head
just been explained. The gaskets (fig. 3-24) that serve as
engines (fig. 3-23) and to the side of the cylinder head
seals between these parts require as much attention
on overhead-valve engines.
during assembly as any other part. It is impractical to
machine all surfaces so that they fit together to form a
In gasoline engines, smooth and efficient engine
perfect seal. The gaskets make a sealed joint that will
performance depends largely on whether or not the
prevent loss of compression, coolant, or lubricant.
fuel-air mixtures that enter each cylinder are uniform in
strength, quality, and degree of vaporization. The inside
The cylinder head gasket is placed between the
walls of the manifold must be smooth to offer little
cylinder head and engine block to maintain a gas, oil,
obstruction to the flow of the fuel-air mixture. The
Figure 3-23.--Intake and exhaust manifolds.