Positive Crankcase Ventilation: Description and Operation

PURPOSE
The Positive Crankcase Ventilation system is used to prevent crankcase vapors from entering the atmosphere and still provide the necessary ventalation to the crankcase.

OPERATION
The crankcase is vented through each cylinder head cover into the intake via a calibrated orfice and a float valve. Ventalation flow changes between closed throttle operation and open throttle operation.

VENTILATION FLOW

Crankcase Ventilation Closed Throttle:

Crankcase Ventilation With Throttle Closed (idle)

Air for crankcase breathing comes from a port in the intake air housing by the throttle body. Air is drawn into the right cylinder head and exits the left cylinder head.

A float valve in the intake air housing is closed at idle. Crankcase pollutants entering the intake air housing are routed through a calibrated orifice in the throttle body.

The calibrated orifice restricts the amount of pollutants entering the intake manifold.

Crankcase Ventilation Part Or Full Throttle:

Crankcase Ventilation With Throttle Open (partial or full load)

When the throttle plates are opened, the float valve in the intake air housing opens.

Crankcase pollutants are now drawn into the intake manifold via both cylinder heads.