The gearbox has also been tweaked to produce even snappier shifts than before, and the car's responses have been altered subtly within the three different drive modes - Normal, Sport and Track - to further increase the driver appeal.
More modifications have been applied to both the soft and hardware of the suspension to sharpen the handling, but at the same time that spookily smooth ride quality that so distinguishes the hydraulically controlled 12C hasn't been compromised in any way.
Instead the car simply feels crisper in its most aggressive setting and even more soothing in its most relaxed modes, says McLaren, providing it with a far broader dynamic repertoire than a 12C.
Outwardly it doesn't take long to pick the 650S out beside a 12C. The new nose treatment has more than a whiff of P1 about it and will, says McLaren, form a key part of the company's design ethos from now on.
You'd have a harder job to spot the differences from the rear mind; apart from a mildly redesigned diffuser and a couple of small new fillets of carbonfibre around the taillights, the 650S looks all but identical to a 12C from behind.
Inside there are several new features that distinguish the 650S; Alcantara becomes the standard trim material, the infotainment centre takes its cues from the P1 and is much more intuitive to use as a result, and if you specify the new carbonfibre sports seats - which cost £5000 (ouch) but are fabulous to sit in - you also shave a not insignificant 15kg from the car's already meagre 1330kg dry weight.
Everything is symmetrically created, so not is neat and tidy to look out, everything is also logically clustered together, which McLaren claims will minimising the time you waste learning where each function is. The portrait infotainment system is much improved over the 12C's with the sat nav far easier to use, although refresh rates are still an issue. Immediately below is the Adaptive Dynamics Panel where you can finetune to the 650S to best suit your driving characteristics.
Carbonfibre ceramic brake discs become standard fitments, as do Pirelli P-Zero Corsa tyres and LED headlights.
When all is said and done with the 650S, performance is what this car is chiefly about. Yes it looks better with its new nose, and yes it's easier to interact with once you have climbed inside but the key thing about the 650S is the way it drives; the way it goes; the immediacy with which it steers, the way it stops and the way it goes around corners. And in all of these areas the 650S is actually quite shocking to begin with in the way it does everything so much better than the 12C.
Its performance doesn't sound that much more potent on paper, not to begin with at any rate; the 0-60mph time has dropped from 3.2sec to 3.0sec while the 0-100mph time has fallen from 6.2sec to 5.7sec.
But when you examine those numbers more closely, especially the zero to 100mph time, you do at least get some idea as to how explosively fast the 650S now feels - because 5.7sec to 100mph is, by any standards and at any price point, ridiculously rapid, bearing in mind that the 650S is rear-wheel drive.
What's so impressive about the 650S, though, is that it backs its titanic new levels of performance with such a mighty set of brakes and such a well rounded set of responses from its steering, gearbox and suspension that it never feels like it has too much poke for its own good. However fast it can go, it can stop, steer, and change gear every bit as well.