In a hydraulic torque converter having a torus of flatness ratio (L/H) within the range 0.82-0.9, the outer and inner contours of the turbine in a meridional plane through the axis of the turbine each comprises a combination of a plurality of circular arcs, wherein the ratios between the radii of the circular arcs constituting said outer contour is substantially less than 2, and the ratios between the radii of the circular arcs constituting said inner contour is substantially less than 2.As a result, fluid flows through the turbine stably without being biased, increasing the velocity of relative flow along the turbine blade, and raising the normal speed ratio at which the absolute flow is in the direction of no impact, enabling a higher stall torque ratio without reduction in efficiency.