Heating the Mixture.

Principles of Gasoline And Disesel Fuel Systems
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vaporization without heating to the point of significantly reducing

volumetric efficiency.

b. Ram Induction. Intake manifolds can be designed to provide optimum

performance for a given engine speed range by varying the length of the

passages. The inertia of the moving intake mixture will cause it to bounce

back and forth in the manifold passage from the end of one intake stroke to

the beginning of the next intake stroke. If the passage is then the proper

length, so that the next intake stroke is just beginning as the mixture is

rebounding, the inertia of the mixture will cause it to ram itself into the

cylinder. This will increase the volumetric efficiency of the engine in the

designated speed range. It should be noted that the ram manifold will serve

no useful purpose outside of its designated speed range.

c. Heating the Mixture. Providing controlled heat for the incoming

mixture is very important for good performance. The heating of the mixture

may be accomplished by one or both of the following:

(1) Directing a portion of the exhaust through a passage in the

intake manifold (figure 8). The heat from the exhaust that is diverted into

the intake manifold heat passage is controlled by a manifold heat control

valve.

FIGURE 8. EXHAUSTHEATED INTAKE MANIFOLD.