The General Electric/Allison J33 is an American centrifugal-flow jet engine, a development of the General Electric J31, enlarged to produce significantly greater thrust, starting at 4,000 lbf (18 kN) and ending at 4,600 lbf (20 kN) with an additional low-altitude boost to 5,400 lbf (24 kN) with water-alcohol injection.