Spiess Tuning is the common identity of Siegfried Spiess Motorenbau GmbH, a motor vehicle engine tuning company based in Ditzingen, Baden-Württemberg, Germany. Today Spiess Tuning is most famous for its Formula 3 motor racing engines based on the Opel Family II and two iterations of Volkswagen R4 engines.
In addition, Spiess has worked on many different engines with motor racing applications, including a 4.0 litre V8 for use in the DTM Opel Vectra.
References
Spiess Tuning Wikipedia(Text) CC BY-SA