Abstract: The disclosure relates to a speed control device for engines and particularly automotive engines so that the throttle or speed control member on the engine may be set to operate the engine and the vehicle at any one of several desired speeds. The device includes a reciprocating member adapted to reciprocate in a rectilinear path in opposite directions and adapted to be coupled to an engine speed control member such as the carburetor throttle of the like and the reciprocable member is coupled to a means for transferring rectilinear motion to rotary motion and this means carries an arcuate row of buttress teeth adapted to be engaged by a pivotal latch pawl which is readily disengagable from the teeth by means of a fluid operated device such as a hydraulic cylinder operable by hydraulic brake fluid so as to automatically release the latch pawl from the buttress teeth when automobile brakes are applied and also a manual control for releasing the latch pawl from the buttress teeth.