Mercedes-Benz plans to increase the output of the SL63 AMG’s twin-turbocharged 5.5-litre V8 direct injection petrol engine from a standard 529bhp to 577bhp from June, the German car maker has revealed.

In a move aimed at streamlining production the SL63 AMG will be available in just one state of engine tune. The performance package option is set to be dropped.

With a new output of 577bhp, the SL63 AMG will pack 48bhp more than today’s standard model and 21bhp more than the existing SL63 AMG with the optional performance package.

Together with the increase in reserves, the SL63 AMG will also receive a mechanical locking differential as standard equipment.

The move will follow the introduction of the SL400, a replacement for the Mercedes-Benz SL350 brought as part of a series of subtle changes brought to the SL line-up. The move is part of a bid to stir sales of the two-year-old luxury roadster.

The SL400 is powered by Mercedes-Benz’s twin-turbocharged 3.0-litre V6 direct injection petrol engine, unveiled in the new E400 early last year. With 328bhp and 354lb ft of torque, it delivers 26bhp and 81lb more than the naturally aspirated 3.5-litre V6 direct-injection petrol unit used by the SL350.

Despite the appearance of a new nine-speed automatic gearbox on selected new Mercedes-Benz models, the new SL400 runs the tried and tested seven-speed automatic. Official performance claims give it a 0-62mph time of 5.2sec – beating the SL350 by 0.7sec – and an electronically limited 155mph top speed.

Combined cycle consumption is put at 39mpg for average CO2 emissions of 172g/km, in the process providing the new SL model with EU6 compliance.