A product comprising: a passage (28, 32, 34, 40, 42, 43, 45, 55, 57) of an engine breathing system and an engine breathing system valve located in said passage to regulate fluid-flow in the passage (28, 32, 34, 40, 42, 43, 45, 55, 57), the engine breathing system valve comprising: a valve body having a port and having a first seating surface lying along a cone outer surface of an imaginary cone, the imaginary cone having a cone center axis which is at an acute angle (Θ) with respect to a center axis of the port so that, in cross-section, a first portion of the first seating surface is at a different angle with respect to the port center axis than a second portion of the first seating surface; a stem rotatably carried by the valve body at a location away from the first seating surface, the stem having an axis of rotation (R 1) being radially offset from the port center axis; and a valve member connected to the stem to rotate about the stem, the valve member having a valve member plane defined parallel to a valve face of the valve member and being, when in a closed position, axially offset from the axis of rotation (R 1); wherein: the valve member comprises a second seating surface that contacts and mates with the first seating surface to form a circumferentially continuous seal when the valve is closed; the valve member has a boss extending away from a valve rear face, the boss defining a passage therein for receiving the stem, and a retaining pin is inserted into the boss and into the stem to connect the stem to the valve member, and a clearance is defined between an outer surface of the stem and an inner surface of the passage, the clearance accommodating relative thermal expansion and contraction between the stem and the boss. a passage (28, 32, 34, 40, 42, 43, 45, 55, 57) of an engine breathing system and an engine breathing system valve located in said passage to regulate fluid-flow in the passage (28, 32, 34, 40, 42, 43, 45, 55, 57), the engine breathing system valve comprising: a valve body having a port and having a first seating surface lying along a cone outer surface of an imaginary cone, the imaginary cone having a cone center axis which is at an acute angle (Θ) with respect to a center axis of the port so that, in cross-section, a first portion of the first seating surface is at a different angle with respect to the port center axis than a second portion of the first seating surface; a stem rotatably carried by the valve body at a location away from the first seating surface, the stem having an axis of rotation (R 1) being radially offset from the port center axis; and a valve member connected to the stem to rotate about the stem, the valve member having a valve member plane defined parallel to a valve face of the valve member and being, when in a closed position, axially offset from the axis of rotation (R 1); wherein: the valve member comprises a second seating surface that contacts and mates with the first seating surface to form a circumferentially continuous seal when the valve is closed; the valve member has a boss extending away from a valve rear face, the boss defining a passage therein for receiving the stem, and a retaining pin is inserted into the boss and into the stem to connect the stem to the valve member, and a clearance is defined between an outer surface of the stem and an inner surface of the passage, the clearance accommodating relative thermal expansion and contraction between the stem and the boss. the valve member comprises a second seating surface that contacts and mates with the first seating surface to form a circumferentially continuous seal when the valve is closed; the valve member has a boss extending away from a valve rear face, the boss defining a passage therein for receiving the stem, and a retaining pin is inserted into the boss and into the stem to connect the stem to the valve member, and a clearance is defined between an outer surface of the stem and an inner surface of the passage, the clearance accommodating relative thermal expansion and contraction between the stem and the boss.