A convertible version was also available, for the first time in 1987, built by Bertone of Torino/Italy, bringing it to line with competitors, such as the Ford Escort and Volkswagen Golf. For the 1988 model, capacities were raised from 1.3 to 1.4 litres. In the fall of 1986 a new 1,998 cc engine replaced the 1.8 hitherto used on the GSi and Vauxhall Astra GTE in many markets, although the 1.8 continued to be sold in some places. In 1988, a 16-valve twin-cam version was developed for a high-performance GSi/GTE model, yielding 156 PS (115 kW) in non-catalyzed form, six less horsepower with a catalytic converter fitted. While criticized for a lack of refinement, the GSi 16V was also lauded as the most powerful car available in its class at the time. Aside from the "16V" badging, it could be told from an eight-valve GSi by its twin rectangular exhaust pipes.
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).