On the older engines, The injectors were in front of the valves. So the engine oil vapor would be washed with fuel before passing over the valves. With direct injection engines. There is no fuel washing the intake valves. Only the oil, which builds up, requiring valve cleanings, if you don’t perform valve cleanings you decrease performance. The catch can catches most of the oil vapor coming from your crank reducing the amount of build up on your valve.
If YouTube t”direct injection catch can” there is a lot of info out there. This isn’t a new issue.
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