Crankcase Vacuum

MOTOR MAGIC                          How to Guide                        






The proper crankcase vacuum will prevent oil burning and leaks.

prevent pollution, and increase horsepower & MPG


The process is very simple- the vapors from the motor are pulled out the PCV valve (high vacuum) and burned in the motor.  Clean air is added through hose A. (low vacuum)- The PCV opens and closes automatically to achieve the desired air flow rate in the crankcase. Hose A also acts as a release if there is excess pressure in the crankcase.  The PCV will also act as a check valve if there is a manifold back fire.

4 cyl engine

Crankcase vacuum is easily measured (with a homemade manometer)

at the top of the dipstick tube.  (see below)


What can go wrong?          1-- wrong size or stuck PCV

                                            2--vacuum leak in hose B

                                                               3-- vapor gunk in the intake manifold


What are the results?             1--the engine will burn large amounts of oil

                                    2--the engine will pollute the air

                    3--loss of horsepower

Homemade Water Manometer (cost $10)


conversion factors:   12 inches of water = .43 psi of vacuum

                                         1" of mercury = .5 psi of vacuum

Note: racing engines require about 4 psi of crankcase vacuum for max hp-


     (note:at full throttle the racing engine has no manifold vacuum)


PCV Valve    (variable orifice)

note: most PCV valves shut off at about 3psi vacuum









































Stay Tuned!      

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