Mercedes-AMG has been spotted testing a modified GT R at the Nürburgring
The car is thought to be a development model for the GT Black Series
The GT Black Series is due on roads in 2020
It's likely to get a more highly tuned version of AMG's turbocharged 4.0-litre V8 engine...
...offering more than 630bhp to beat the current most potent AMG V8, the GT 4-door Coupé
Mercedes-AMG boss Tobias Moers confirmed that a Black Series was coming in 2016
AMG's engineers are now testing new lightweight parts for the most extreme GT variant
These include a polycarbonate rear window and pared-back interior
The future range-topping car, first confirmed back in 2016 by AMG boss Tobias Moers, is now under development and is pipped to receive AMG's turbocharged 4.0-litre V8 engine in a state of tune offering at least 630bhp.
This is the figure offered by the current most powerful AMG model with that unit, the recently revealed GT 4-door Coupé. Any growth on that would ensure the Black Series dwarfs the peak output offered by the current GT champion, the 577bhp GT R. It would also edge it towards one of the category's most radical supercars, the 690bhp Porsche 911 GT2 RS.