poppet intake valve or crank case entry ports however numerous differences would of course occur in structure and function between the rotary valve generally indicated as 10 in the present invention and that of the intake manifold in order to keep the diameter of the rotor 64 to an economic minimum thus reducing the rubbing velocity and the rotary movement of inertia to as low values as feasible the outlet apertures 70 from the rotor 64 entering the valve body passages 72 will be elongated in the axial direction the ratio of axial to tangential dimension will be nominally 2 and one half to 1 with the long edges parallel to each other and the axis of the rotor 64 and with the 34 following 34 or cutoff edges exactly cut at the correct cutoff angle on 90 degree spacings the short sides of passage openings will be in parallel planes at right angles to the axis of the rotor 64 the passages 72 in valve body 67 will transform from these rectangular openings to match the intake valve or crank case port openings which are usually more curcular or square for material and flow economy reasons the carburetor 18 would mount on a standard flange near the center of the rotary valve body 67 the passage connecting the carburetor throat outlet will 34 transize 34 to a ring shaped passage 74 in the valve body 67 which will encircle the rotor 64 and via the rotor inlet apertures 68 provide continuous free communication of flow from the throat of the carburetor into the interior 66 of the rotor 64.