You won't really decrease crankcase pressure at all with the breather. Rather, you will just vent it to the atmosphere instead of back into the intake which is a good thing. Like baabootoo said, it was removed in the 60/70's from cars so that we would not be venting these oil fumes and other gases directly into the air. In doing this you will keep some heat out of the intake but better yet, any engine oil from being introduced into the cylinders above the rings. A big issue with introducing oil is that not only does it gum stuff up and interfere with the combustion process of gasoline/ethanol as these engines were designed, it also lowers octane level as oil has a lower rating. See you are a genius.
Did I hear that you run 100 octane 100% of the time?
Did I hear that you run 100 octane 100% of the time?