Mercedes-AMG downsizes V8

MERCEDES-AMG will dramatically downsize the displacement and consumption of its staple big-bore V8 this year when an all-new and substantially more powerful petrol engine replaces AMG’s 6.2-litre bent eight.

The new 5.5-litre engine, revealed just before last week’s Geneva motor show opening in a new S63 AMG concept car, will make its debut in the facelifted CL-class coupe, which will echo the CLK-replacing E-class Coupe by being named the S-class Coupe when it goes on sale in Australia in the fourth quarter of this year.

Set to continue with a ‘63’ model designation despite its smaller capacity, the new AMG V8 incorporates direct fuel-injection, double overhead camshafts and, marking a return to forced induction and a departure from an engine AMG claims is the world’s most powerful naturally aspirated V8, a pair of Garrett turbochargers.

Peak power is quoted at 400kW at 5500rpm (versus 386kW ay 6800rpm for AMG’s current 6.2 V8), while maximum torque increases by a more substantial 170Nm, from ‘just’ 630Nm to a massive 800Nm between just 2000rpm and 4500pm – rather than at 5500rpm in the 6.2.

An even more hairy-chested version of the new ‘M157’ V8 will also be offered as a ‘Performance Package’ upgrade, at least overseas. It delivers no less than 420kW and 900Nm – the latter from just 2500rpm – but will not be available in Australia.

While the ‘garden-variety’ 400kW V8 employs air-to-water intercooling with maximum boost pressure of 1.0 bar, the 420kW version delivers 1.3 bar of boost pressure, also aided piezo-electric injectors.

Fitted to the S-class, the M157 delivers 0-100km/h acceleration in a claimed 4.5 seconds, or 4.4 seconds in high-performance guise – up to two-tenths quicker than before.

At the same time, the M157 incorporates an idle-stop function and cylinder shut-down technology like that fitted to other Mercedes models to reduce average fuel consumption by a massive 25 per cent - or a whole four litres per 100km - compared to the current S63.

It’s claimed to return just 10.5L/100km in the newest S63, while average CO2 emissions are stated at 246 grams per kilometre.

Weighing just 204kg, the 747cc-smaller new biturbo V8, which is built at AMG's facility in Affalterbach, will be mated as standard to a variation of the seven-speed MCT Speedshift automatic transmission with wet start-up clutch, as seen in the SL63 and E63.

Rather than being related to Mercedes’ current M155-series 5.5-litre V8, AMG’s new engine is based on a new twin-turbo 4.6-litre V8, codenamed M278, that will become available in the S-class and new CLS-class globally later this year.

Officially, the M157 is not a direct replacement for the current 6.2-litre M156, but is designed as another engine option for AMG customers, which can also select the 450kW/1000Nm 6.0-litre twin-turbo petrol V12 that powers the S65, SL65 and CL65.

A naturally aspirated version of the M157 is also rumoured to power the next generation of smaller AMG models such as the C-class, but GoAuto understands either the atmo or biturbo 5.5 will eventually replace the atmo 6.2 in every AMG model, including the C63, E63, CLS63, S63, CL63, SL63 and ML63.

As well as following an industry-wide shift towards smaller-capacity forced-induction powerplants, the move mimics BMW’s shift from a 5.0-litre V10 to a twin-turbo 4.4-litre V8 for BMW’s largest M models.

The TTV8 also marks the first force-fed V8 from Mercedes since the supercharged 5.4-litre V8 that preceded the 6.2 V8. A dry-sump, freer-breathing variation (M159) of the first AMG V8 to be fully designed in-house also powers this year’s SLS AMG super-coupe.

The S63 concept revealed pre-Geneva was draped in the livery of Mercedes’ 6.8-litre 1971 300SEL AMG racing car and appeared with a number of styling cues that are likely to feature on AMG’s updated S63, including even more prominent side sills and rear wheel-arches.

"With the new AMG V8 biturbo engine and the AMG Speedshift MCT seven-speed sports transmission, we are confronting the challenges of the future and focussing on fuel consumption and exhaust emissions even more intensively than before," said Mercedes-AMG chairman Volker Mornhinweg.

"Our new high-performance engine shows that AMG occupies a leading position in terms of both efficiency and our brand commitment to performance."