In a hydraulic torque converter having a torus (10) of flatness ratio (L/H) within the range 0.82 - 0.9, the outer and inner contours of the turbine (6) in a meridional plane through the axis of the turbine each comprises a combination of a plurality of circular arcs (A,B,C and D,L respectively) wherein the ratios (B/C, B/A, C/A) between the radii of the circular arcs constituting the outer contour is subs­tantially less than 2, and the ratio (E/D) between the radii of the circular arcs constituting the inner contour is also 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.