catch cans on the road are illegal (in Vic) as they do not allow the
vehicle to comply with ADR and EPA regs...and the cops do check.
A sealed catch can is a fire hazard as they fill with oil fumes
..and where do the fumes go? At least a PCV valve re-circulates
the oil fumes back into the inlet manifold...when it least affects
performance
An unsealed or vented catch can is just another receptable (same as your rocker covers)
to hold oil fumes before they are vented to atmosphere ...which is illegal on road cars since
the mid 70s. Vented catch cans are seen on race cars...as they don't need to comply with EPA regs
and and they do provide EXTRA room for engine gases and fumes.
Catch cans on CAMS registered vehicles or vehicles used in CAMS sanctioned events
must be at LEAST 3 litre capacity (on V8 vehicles)
hth
Smitty