Available from July, the new offers 125kW from 4250rpm and 280Nm of torque between 1650-4250rpm. Those figures mark a 7kW drop in power, but a handy 50Nm boost in torque.
The engine is available only in automatic form however, paired with a new low-friction six-speed transmission and priced at $36,990 plus on-roads.
The $34,990 manual Astra GTC will continue with GM's existing 1.6 turbo engine, producing 132kW and 230Nm.
The manual remains the quicker car, hitting 100km/h in 8.3 seconds while the auto gets there in a more stately 9.2 seconds.
If fuel consumption is your priority however, the auto is the pick at 8.9 l/100km, compared to 9.5 l/100km for the manual.
Standard features with both GTC models include Opel’s sport chassis setup and HiPerStrut front suspension, AGR heated front sports seats and Mondial leather appointed trim throughout the cabin.
There's also climate control, Bluetooth/USB/iPod connectivity, auto-on headlamps, foglamps, rain-sensing wipers, a trip computer and front and rear parking sensors. Bi-xenon headlamps are available as a cost option.
The GTC models also get satellite navigation and a 7-inch colour infotainment screen.
The new auto GTC is available from July, and the manual model (see our review here) is available now.