This AV is for the purpose of installing the engine sound profile for the Hirtenberger Patronen VT-21, one of the smallest four stroke engines commercially produced. At the time, it was the smallest until O.S. Engines eclipsed it with the FS-20.
Although a four cycle engine, it does not have traditional valves so the engine has a very distinct and unique sound all its own.
This engine sound profile is made from an audio clip of my personal VT-21 mounted on a test stand.
