Can creating too much crankcase vacuum be bad? I had one pvc in the valve cover and the other side blocked off and it created quite alot of vacuum, can this harm anything?

 

will create a vacuum lock on the motor making it harder to turn the crank. also start sucking up more oil than normal. need a breather on the one side you capped off. to keep pressure equal inside the motor.

 

Actually, running the crankcase in a deep vacuum can be a good thing, other than it tends to draw hot combustion gasses into the case. The lower air mass in the case would theoretically create less aerodynamic drag on the rotating assembly. As for making it harder to turn the crank, pressure variation in a case is basically neutral, since as one piston travels downward, another is traveling upward at exactly the same rate. All eight (or six, four, etc.) cylinders balance each other in terms of crankcase pressure. I wonder how well that works on one of those 5-cylinder Vulvos. ?? Or a 3-cylinder Geo Sprint. Then again, if you have either of those, you have other issues to worry about...