====== Induction and Exhaust System ======
This article is part of the [[engine]] and power unit section\\
The induction and exhaust system deals with the inflow of fresh gases and outflow of used gases in the engine.

===== Induction System =====
Fuel air mixture flow from the carburetor, or throttle body, towards the combustion chamber, is through the Induction System which consists of the following parts:
  * Induction manifold. Which provides passage for the flow of fresh gases from the carburetor, or throttle body, towards combustion chamber.
  * Intake port. Passage leading from induction manifold to combustion chamber and on which end is housed the Intake Valve.
  * Intake Valve. The valve which provides entrance for fresh gases towards combustion chamber.

===== Exhaust System =====
Used gases are expelled out of combustion chamber through the exhaust system which contains the following parts:
  * Exhaust Valve. Which serves as a gate for the outflow of used gases from the combustion chamber.
  * Exhaust Port. The passage through which used gases go out from the combustion chamber to the exhaust manifold.
  * Exhaust Manifold. The exhaust manifold provides a passage for the outflow of exhaust gases.
  * Exhaust Pipe, Muffler, Tail Pipe. These constitute the main parts of the silencer with the help of which noise of outgoing exhaust gases is decreased.
==== Muffler ====
The muffler quiets the noise of exhaust gases by reducing the pressure of used gases by slow expansion and cooling. This is attained with the aid of a number of expanding chambers. The gas is allowed to expand from the first passage into a much larger second one and then to a still larger connected to the tail (outlet) pipe of the muffler.
==== Induction and Exhaust Manifold ====
In majority of the larger engines induction, and exhaust manifolds are combined into one unit. A portion of the induction manifold is made to pass through the exhaust manifold so that the exhaust hot gases may heat that portion of the induction manifold which is know as //hot spot//. Due to //hot spot//, the ingoing fresh gases are saved from converting to liquid. IT also pre-heats the ingoing mixture for easy combustion.
==== Heat Control Valve ====
The heat control valve is thermostatically or mechanically operated valve, which is fitted in the combined Induction and Exhaust Manifold. This valve allows the exhaust gases either to pass around the //hot spot// or below the //hot spot//.

In case of thermostatically operated heat control valve, the valve does not let the exhaust hot gases pass below the induction manifold tube unless the temperature reaches a cetain degree when the valve begins to open. During this period the hot gases pass around the //hot spot// heating the ingoing fresh mixture in the induction manifold.