The Sauer S 2100 ULT is a turbocharged four-stroke aircraft engine for homebuilt and ultralight aircraft.[1]
The engine is based on the Wasserboxer. It is extensively modified for aircraft use and all the parts are custom made. The engine is derived from the certified engines produced by the same manufacturer and used in several motorgliders and light aircraft.
At least one Asso X is reported to be using this engine.[2]