yup the vacuum actually pulls the crankcase pressure/vapors out of the crankcase and is able to burn in the combustion chambers.... i've seen cars without a pcv run terrible.... my buddy got a fully restored 66 charger for $2500 because of this... the guy built the car and dumped thousands into it, rebuilt the 440 and everything but just couldn't get it to run right, he finally got so frustrated he sold it to my friend for $2500.... my friend added a pcv to the car and it now runs like its brand new