During the 1930s, the Rüsselsheim plant was never given a major role in Germany's war preparations. Neither was Ford's plant in Cologne considered trustworthy enough for a big assignment, such as tank manufacture, in view of their earlier foreign associations. Initially, of course, the war was thought to be a short one settled in Germany's favour. Auto plants were shut down, to conserve resources, but not converted to other jobs. As was common with much of the production in Nazi Germany during the war, slave labor of deported civilians and Soviet POWs was utilized in the Opel factories.
Many Opel models or models based on Opel architectures have been sold in Australia and New Zealand under the Holden marque, such as the Holden Barina (1994-2005), which were rebadged versions of the Opel Corsa, the Holden Astra. a version of the Opel Astra, and the Captiva 5, a version of the Opel Antara. In New Zealand, the Opel Kadett and Ascona were sold as niche models by General Motors New Zealand in the 1980s, while the Opel brand was used on the Opel Vectra until 1994.
The GSi's engine mapping had been carried out by Opel tuning specialists Irmscher. A model with the 82 PS (60 kW) 1.4 L multi point fuel injected engine, which was otherwise mechanically identical to the GSi, also became available as the Nova SRi in the United Kingdom. In January 1988, a turbocharged version of the Isuzu diesel engine was introduced, with power increased to 67 PS (49 kW).