Abstract: A Roots-type supercharger 100, 1100 includes a housing 120, 1120, a first rotor 200, a second rotor 300, an outlet volume 400, a transfer volume 500, and a bleed port 600, 600?, 1600. The housing includes an interior chamber 130, an inlet port 140, and an outlet port 150, 1150. The first rotor 200 and the second rotor 300 have a plurality of lobes 210, 310, respectively. The outlet volume 400 is substantially bounded between the outlet port, the first rotor, the second rotor, and the interior chamber of the housing. The transfer volume 500 is substantially bounded between the first rotor, the second rotor, and the interior chamber of the housing. The bleed port 600, 600?, 1600 is adapted to fluidly connect the outlet volume and the transfer volume at least during a portion of a transfer volume cycle. The variable bleed port may include a plate that pivots about a pivot or slides along a slide. The plate may be arc shaped and may arc around a centerline of one of the rotors.