A cylindrical valve assembly, including: a housing defining a port, an interior volume, and an interior surface; a lip structure disposed about the periphery of the port, wherein the lip structure protrudes into the interior volume past the interior surface of the housing; and a valve door defining an exterior surface disposed concentrically within the housing, wherein the valve door is configured to move from an open configuration in which it does not obstruct the port to a closed configuration in which it does obstruct the port, and wherein, when the valve door is in the closed configuration, the exterior surface of the valve door is in contact with the lip structure and not the interior surface of the housing. Optionally, the lip structure is provided by an insert structure that is disposed through the port. Optionally, an end of the insert structure opposite the lip structure includes a velocity stack. Optionally, a plurality of dimples are manufactured into the exterior surface of the valve door.

Embodiments of the present disclosure present a valve assembly that includes a valve body having a gas passage bore, a valving bore extending along a longitudinal axis and intersecting the gas passage bore, a first bearing surface concentric with the longitudinal axis and a radially spaced apart second bearing surface concentric with the longitudinal axis, wherein an interface of the gas passage bore and the valving bore defines a flow port radially intermediate the first bearing surface and the second bearing surface. The valve assembly further includes a shaft valve extending along the longitudinal axis and rotatably mounted in the valving bore.

A road vehicle with an endothermic engine comprising an air intake duct for introducing air into at least one combustion chamber; wherein there is provided in the air intake duct a device for selectively generating a tumble of air in the combustion chamber; wherein the device for selectively generating a tumble consists of a single fin arranged within the air intake duct; in which the fin is shaped as a corresponding portion of the inner surface of the intake duct and is movable between a rest position, in which it is substantially entirely in contact with the corresponding portion of the inner surface of the intake duct and does not interfere with the flow of air passing through the intake duct, and a plurality of working positions in which it progressively penetrates the intake duct to convey the flow of air passing through only at a portion of the intake duct.

A road vehicle with an endothermic engine comprising an air intake duct for introducing air into at least one combustion chamber; wherein there is provided in the air intake duct a device for selectively generating a tumble of air in the combustion chamber; wherein the device for selectively generating a tumble consists of a single fin arranged within the air intake duct; in which the fin is shaped as a corresponding portion of the inner surface of the intake duct and is movable between a rest position, in which it is substantially entirely in contact with the corresponding portion of the inner surface of the intake duct and does not interfere with the flow of air passing through the intake duct, and a plurality of working positions in which it progressively penetrates the intake duct to convey the flow of air passing through only at a portion of the intake duct.