The O.S. Max FS-1.20 Surpass SP (supercharged) used a Roots-type blower and did produce a lot of power. It was designed for the FAI Pattern airplanes of the time. It could be temperamental at times, and would usually need to have about 5 gallons of fuel run through it before it really "came in" and began to handle well. I knew several flyers who loved them. There was one group that used them in 1/4-scale pylon racing and were quite disappointed when O.S. ceased production of the engine.