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AMG’s bonkers new flat-plane V8 explained

By Cameron Kirby, 15 Jul 2020 History of Turbo

AMG’s bonkers new flat-plane V8 explained

The crew at Affalterbach have gone to town on AMG’s venerable 4.0-litre twin-turbo V8

The first Black Series model in eight years has finally been revealed and it's just the second turbocharged model in Black Series history, and the first boosted V8.

However, simply slotting in a slightly tweaked version of AMG’s venerable M177/178 4.0-litre V8 under the bonnet wasn’t going to cut it.

So, while the Black Series does utilise a similar core layout of a 4.0-litre V8 with two turbochargers nestled within the cylinder banks, AMG engineers have gone to town refining the powerhouse engine into something new altogether.

Read next: How GM lost $23 million building an orphan V8

So extensive is the work, that AMG has given the engine a new internal designation of M178 LS2.

Official outputs for the Black Series’ engine are 537kW at 6700-6900rpm, and 800Nm in a massive powerband between 2000-6000rpm. For context, that’s a massive 107kW/100Nm more than what is on tap in the AMG GT R.

What’s new? Well, the biggest change is a move to a flat-plane crank design – the first of its kind in AMG’s history.

This helps the compact V8 have a more responsive character and rev harder, with redline jumping 200 revolutions per minute to 7200rpm. This more potent peak power figure compared to the GT R arrives 500rpm later.

Another side effect of the move to a flat-plane crankshaft is a new firing order. The 4.0-litre V8 now jumps between cylinder banks, with a 1-8-2-7-4-5-3-6 firing order. This creates uniformly oscillating gas columns which generate a predictable flow of gases through to the turbochargers.

Expect the GT R Black Series to sound very different to previous GT Rs as a result, with harder-edged top end acoustics, albeit at the cost of typical cross-plane V8 woofle  and torque at lower revs. The flat-plane crank also generally delivers crisper throttle response.

Read next: AMG has just changed the turbo game

AMG engineers have tweaked the compression ratio, and fitted new twin-scroll turbos with ball bearings for which ought to further improve throttle reactions – the same found in the AMG GT 4 Door.

However, the Black Series turbos have a larger compressor wheel, capable of shifting 1100kg of air per hour (up from 900kg per hour in the GT R.

Boost has also been increased. Where a regular GT runs 1.2bar and a GT R has 1.35, the Black Series winds up the boost the 1.7bar.

The dry sump engine also has new camshafts and exhaust manifolds, and larger intercoolers for better heat management.

Here at Wheels HQ we are big fans of the M177/178 lump – going so far as to naming it one of the greatest V8 engines ever built.

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