It’s actually the exact opposite. High vacuum and blow by is what causes oil in the catch can. The catch can is installed in the vacuum line from the PCV valve to the intake, as the engine runs vacuum opens the PCV valve and the vacuum from the intake pulls crankcase vapors and pressure into the intake to be reburned, catch can just filters out about 50% of the oil vapor causing it to condense where it’s too heavy to be pulled by the air and it falls into the container. When you go heavy throttle the PCV valve essentially shuts as and engine produces very little if not 0” of vacuum at high load WOT so pressure in the crank case gets pushed out the “breather” side of the PCV which connects into the cold air intake by the filter. Pressure will push out along with oil vapor into the intake tube and still make its way into the engine and TB. But it won’t be going into the catch can. There is also a slight suction on the intake tube PCV port at WOT as air is rushing past the port causing a slight vacuum.
High vacuum or low load is where most oil will accumulate in the catch can. So daily driving, city and highway.
Honestly the best option Is to put a catch can and the. Put a breather overflow on the fresh air side to catch any oil that makes it out when your goosing it. Not 100% neccessary tho as I just run the filter that came with my vararam. But I run the diablo catch can for our trucks and it’s a nice piece, been on 2 trucks and I pull a few ounces out every 3k as I check it every couple of months depending on mileage.
