The engine came with a choice from two power levels. For the standard 1.0 litre engine maximum output was listed as 40 PS (29 kW) at 5,000 rpm, and in October 1963 the high compression "1.0 S-Motor" was added, sharing the 993 cc capacity of the original power unit, but offering a maximum 48 PS (35 kW) of power at 5,400 rpm. The more powerful "S-Motor" engine featured modifications to the inlet manifold, cylinders and camshaft along with a carburetor employing larger (36 mm (1.4 in) diameter than the 30 mm (1.2 in) used on the standard engine. This came with an 8.8: 1 compression ratio whereas the 40 PS (29 kW; 39 hp) engine used a compression ratio of only 7.8 : 1. Higher compression ratios for performance versions of standard engines were a growing trend in West Germany in the 1960s, led by Opel and Ford, and made possible by the growing availability of higher octane "Super" grade fuel at filling stations.
It had some crazy mechanical issues. At one point it stumbled and stalled because the carburetor had come loose from the intake manifold and I had to tighten it back down! Another time, my brother was driving it and the brakes failed. Somehow the end of the brake shoe that meets the brake cylinder piston had become worn on one side, causing the piston to slip off the end of the shoe when the brakes were applied, losing braking and squirting fluid all over.
In addition to its West German home market, the Kadett A sold strongly in what were becoming the manufacturer's traditional export strongholds (notably in Benelux, Scandinavia, Austria and Switzerland). Between February 1964 and the Autumn/Fall of 1965 the cars were also exported to the United States where they were sold through approximately 500 Buick dealers. The same 993 cc engine was fitted and it is not clear whether it was differently tuned for North America: horsepower ratings were differently computed in the USA, following locally devised "SAE" rules: for American market purposes the maximum outputs for the engines were quoted as 46 hp (34 kW; 47 PS) and 54 hp (40 kW; 55 PS).
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).