Quote:
Originally Posted by Mikeez
Anyways, the engine releases the bad gases down the pipes and out the muffler. The cat cleans a % of it... Correct?
What is then the purpose of a catch can and wouldn't it make all of them illegal if the purpose was to collect water vapor?!?
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You are confusing two things. The gasoline engine combustion process isn't perfect, so it releases harmful gasses. Those are absorbed by the cat and what is left goes out the tailpipe and is measured during an emissions check. That has nothing to do with a catch can or the positive crankcase pressure issue. That is caused by combustion gasses getting past the piston rings. The engine needs to have a way to relieve that pressure which is normally a PCV system where those gasses go back into the intake manifold to be burned as part of the normal combustion process. With a vented catch can you just vent those gasses to the atmosphere instead of sending them to the intake manifold.