The GLS 63 heads an increasingly long line-up of go-fast SUVs from Mercedes-AMG.
The US-produced model builds on standard versions of the third-generation GLS with the latest iteration of the Mercedes performance car division’s twin-turbocharged 4.0-litre petrol engine. The sonorous V8 is mated to a 48V mild-hybrid system that enables electric boosting for an extra dose of performance and greater efficiency.
Driving through AMG’s nine-speed automatic gearbox and a fully variable 4Matic+ four-wheel drive system, the combustion engine kicks out a nominal 603bhp at 5750rpm. A further 22bhp from the electric motor, which also acts as an alternator to harvest kinetic energy, ultimately gives the GLS 63 a combined 625bhp. That's 48bhp more than the now-discontinued 5.5-litre twin-turbo V8 engine found in the old GL 63.
Torque is rated at 626lb ft between 2250rpm and 5000rpm, although it can be boosted to 810lb ft for short periods of full-throttle acceleration thanks to an additional 184lb ft from the electric motor.
Official figures point to a 0-62mph time of 4.2sec and a nominal top speed of 155mph. This can be raised to 174mph with the optional Driver’s Package, which also adds upgraded tyres to the mix.
A range of fuel-saving features, including a coast function that idles the engine on a trailing throttle and brake energy recuperation, aim to provide the 2555kg GLS 63 with creditable fuel consumption and emissions figures, but with claimed combined cycle figures of 23.7mpg and 273g/km on the WLTP test procedure, it’s anything but economical.