Mercedes-AMG GT to get new 503bhp twin-turbo engine

The upcoming Mercedes-AMG GT will be powered by a twin-turbocharged four-valve-per-cylinder 4.0-litre V8 petrol engine, the German carmaker has officially confirmed.

In its initial state of tune, the unit will develop 503bhp at 6250rpm and 66.22kgm of torque on a band of revs between 1750 and 4750rpm.

The all-new 90-degree quad-cam direct-injection unit, known internally under the codename M178, has been developed from the ground up as a replacement for AMG’s existing naturally aspirated 6.2-litre V8, the M159, which is being phased out after four years, following the end of production of the SLS AMG in both coupé and roadster guises.

AMG’s new sand-cast aluminium block engine, also slated to power the upcoming replacement for the C63 AMG, boasts the same 83mm and 92mm bore and stroke measurements as the Mercedes-Benz performance car division’s 355bhp turbocharged 2.0-litre four-cylinder direct-injection powerplant, as used by the A45 AMG and CLA45 AMG, giving it an overall swept volume of 3982cc.

Boosting induction are a pair of Borg Warner produced turbochargers mounted atop the engine within the space between the two cylinder banks – a layout AMG engine boss, Christian Enderle, says helps make the M178 some 88mm shorter than the M159 engine. 

Other technology included on AMG’s second turbocharged production car engine is a Bosch-supplied piezo injection system, capable of providing up to seven individual injections per cycle, cylinder barrels finished with Mercedes-Benz’s patented Nanoslide friction reducing material, a cylinder head produced from a lightly Zirconium-refined aluminium and dry sump lubrication.

The exhaust is rooted from the turbochargers high up in the middle of the engine, providing the M178 with what is known as a 'hot inner vee'. Initial aural impressions of the new powerplant on a test bed at AMG’s headquarters in Affalterbach, Germany, reveal it retains the characteristic baritone exhaust note as its predecessor.

With a specific output of 126.3bhp per litre, the turbocharged M178 engine slated for the new GT develops a significant 35.6bhp more per litre than the naturally aspirated M159 unit fitted to the standard SLS AMG.

But with a swept volume that is a considerable 2226cc less than its predecessor, its overall 503bhp is down by 65bhp on the engine it replaces in its initial state of tune. Peak power is also developed 750rpm earlier in the rev range at 6250rpm.

The new AMG engine’s 66.22kgm of torque is the same as that offered by the standard M159 unit. However, it is developed 3000rpm earlier in the rev range at 1750rpm and continues on a plateau through to 4750rpm.

By comparison, BMW M division’s twin turbocharged 4.4-litre V8 direct-injection petrol engine, as used by the M5, M6 coupe and M6 cabriolet, boasts 125.6bhp per litre for an overall 552bhp at 6000rpm and 69.26kgm  of torque from 1500 through 5750rpm.