AMG’s flatplane crank
Want more revs and sharper responses from your V8? Then you need a flatplane crank.
The Black Series is a very special AMG GT. That much is made abundantly clear by the way it looks (see below for a reminder) and its price – £335k last time we checked (which was just moments ago; we’re a little obsessed with the new Black Series). From an engineering standpoint that toppy list price opens up a world of possibilities, from exotic materials ill-suited to series production on a budget to, well, to replacing or modifying the lion’s share of the engine in search of more power and a sharper throttle response… Which is precisely what AMG’s done.
FIRST, THE SCIENCE
AMG’s non-Black Series V8 uses a crossplane crankshaft. The name refers to the appearance of the crankshaft when viewed from either end: the crankpins (the points at which the conrods mount to the crankshaft) are arranged at 90° to each other, giving the crankshaft a cross-like appearance should you look down it. The result is the classic V8 burble and rich, lazy power.
But there is another way, as you’ll know if you’ve been anywhere near something like a Ferrari 458 Speciale at full chat: no burble, searing revs, big power. That alternative crank design is the flatplane crank (180° between the crankpins makes the crankshaft appear flat when viewed from either end), and its advantages prompted AMG to turn its V8 from a crossplane engine into a flatplane one for the AMG GT Black Series.
MORE POWER, SHARPER RESPONSES
‘The pros are better response and more power [the Black Series version of AMG’s 4.0-litre V8 makes 710bhp, versus 577bhp for the GT R’s] as a result of better gas exchange and reduced mass inertia,’ explains AMG engine development bon Sven Mueller. ‘The bore and stroke are the same but many parts are modified, including the pistons, camshafts, turbochargers, charge air lines and the intercooler. The main advantage is that the new crankshaft makes the gas exchange more harmonious, eliminating the exhaust scavenging problem of the crossplane V8. In the Black Series engine, a homogeneous combustion in all cylinders allows us to increase the performance potential of the engine, together with a more agile throttle response.’
This is AMG’s first flatplane crank V8. Given the advantages, we don’t expect it to be its last.