Mercedes-Benz has begun the sensitive issue of replacing its much vaunted 6.2l V8 AMG models with turbocharged power.Both the revised CL and current S-Class have been confirmed with biturbo derivatives of the legendary AMG 63 nameplate.The M156 naturally aspirated V8 has been the mainstay of AMG model range since its debut back in 2006.Thanks to the vision of both product planners and engineers at Affalterbach, AMG was able to market a range of vehicles (sedans, coupes and even SUVs) with tweaked versions of essentially one engine architecture, the M156. An increasingly severe regulatory environment regarding emissions has forced AMG’s hand in terms of forced-induction though. The same state of affairs has seen BMW’s M-division forsake high-revving naturally aspirated power for turbocharging.AMG’s solution is the M157 engine. Despite being smaller than the unit displaces, the new 5.5l M157 engine retains the M156 6.2’s oversquare internal architecture. New mechanical design features include twin-turbos with air and water cooling, piezo actuated direct injection and a ventilated aluminium sub-assembly. Instead of employing variable compression turbochargers, the M157 engine’s boost requirement is fed by a simple Garrett-Honeywell turbo per cylinder bank. For a large capacity turbocharged engine compression appear a little on the high side (10.0:1), yet an AMG engineered air-to-liquid intercooler unit chills inlet temperatures down to around 90-degrees.The new engine is based on Merc’s M278 4.6L V8 gaining an AMG block, sump and cylinder head. Its exhaust manifold is joined directly onto the turbocharger housing, ensuring the shortest (most efficient) gas-exchange driven boost path possible. Output figures are wholly impressive. The M157 offers an increase in power of 14kW over the M156 engine, with peak rotational force swelling by an immense 170Nm. Producing 400kW at 5 500r/min (and 800Nm at 2 000r/min) this new AMG engine would appear to be, statistically, a superb replacement for the M156. Powering the rear wheels via a new version of the seven-speed Mercedes-Benz MCT transmission (actuated by a we start-up clutch instead of a torque converter), AMG claims a benchmark 0-100km/h figure of 4.5 seconds for both the new S- and CL63 applications. If customers require more power, AMG is happy to oblige with an optional performance pack for the M157 engine. A recalibrated boost regime (upping pressure from 1- to 1.3bar) and harmonised engine electronics extract 20 additional units of power and 100Nm more torque. Suffice to say, the performance pack AMG S- and CL63 models boast power outputs matching (and toque figures in excess of ) the current SLS AMG.Beyond the rampant performance credentials, AMG’s new bi-turbo V8 is appreciably more efficient than the naturally aspirated engine it replaces. On demand ancillaries and stop-start functionally help reduce overall consumption to a claimed average of 10.5l/100km, an improvement of 3.9l/100km.To ensure the dynamic driving package is as balanced as possible AMG’s new turbocharged S- and CL63 models feature torque-vectoring ESP intervention, shoring up agility.With more power, a keener transmission and a lower emissions footprint these new turbocharged 63-monikered AMGs remain the rear-wheel drive executive expresses of choice for well heeled hooligans. AMG technicians have done their utmost to ensure the new turbocharged CL- and S63 cars retain the legendary acoustic signature of their naturally-aspirated predecessors. Beyond these new 5.5l biturbo models, the CL and S-Class AMG offerings will be bolstered by revised 6l V12 derivatives come September - boasting 463kW.Can the new AMG biturbo V8 recapture the unique character of the M156 6.2l V8?