Before the PCV valve was invented, engines would use ‘downdraft’ or ‘road-draft’ tubes to ventilate the crankcase. As the vehicle drives down the road, a low pressure zone is created at ...

All engines allow some exhaust gases ... which is a source of varying air pressure, the PCV valve maintains the optimal level of vacuum in the crankcase to extract the products of blow-by as ...

While the poppet valves work well at low speeds, they are unreliable at high engine speeds, and the “timing,” or opening and closing of the valves, is uncertain. This is the gravest objection ...