Abstract: An intake manifold for internal combustion engines has a plurality of independent runners emanating from a central plenum. Different sets of runners have different cross-sectional areas matched to flow velocity through the manifold at maximum torque and desired engine speeds to produce a wide high torque band. The length of each runner of each set corresponds to a harmonic frequency of the fundamental frequency of air at standard temperature, but the frequency differs for each runner set. Within each set, runner cross-sectional areas are constant throughout their length. In one embodiment, the runners curve from a plenum to their exits and in the curve each runner's cross section is regular trapezoidal with the small side of the trapezoid on the inside curve and the shape of the trapezoid effecting constant static pressure throughout the cross section.

Abstract: Independent runners of a multiple runner manifold feed from two independent plenums. Alternate runners, in the sense of engine firing order, feed from alternate of the plenums. The physical separation of the plenums attenuates intercylinder interference. Long runners of small cross section provide large mixture quantity and high mixture velocity for good torque. Runner cross-sectional area also is determined by that mixture velocity at which maximum torque occurs. The runners are tuned to the first harmonic to correspond to optimum torque. The runners of one plenum pass over the runners of the other so that runner geometry is simple.