The 2.8-litre turbo, available in Design or Elite trim, is available from £23,050, and now comes with an uprated V6 powerplant, developing 250bhp. The new engines give the Signum a new 0-62mph time of 6.8 seconds and an electronically limited top speed of 155mph.
Design trim models come with a six-speed manual gearbox. The Elite trim comes with a new six-speed automatic transmission.
Both models come with ESP-plus as standard, while the Design gets lowered and uprated sports suspension.
Standard equipment on all Signum models includes colour sat nav, 17-inch alloy wheels and electrically operated front and rear windows. The Design also has front fog lamps, dark-style head and tail lights, half-leather trim, automatic lighting control, rain-sensitive windscreen wipers and active head restraints, while Elite models get full leather trim and electronic climate control.
The new models join the range immediately.