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The Collaborative International Dictionary

blowby \blow"by`\, blow-by \blow"-by`\(bl[=o]"b[imac]`), n. the leakage of gases from the combustion cylinder of an internal combustion engine between the piston and cylinder wall into the crankcase.


n. (context automotive English) in an, any burnt or unburnt matter escaping from the cylinder, past the (worn) rings on the piston, and into the crankcase.