M3 and M4: without the head-up display added, the windscreen shade band is £60 on the four-door but standard on the coupe.
OK, there's a little more than that. Performance stats and technical features are identical for both cars but the saloon is £460 cheaper, 23kg heavier, 7mm wider, 47mm higher, has 58mm more shoulder room in the back and another 35 litres of boot space. Power to weight for a comparable M DCT equipped car is slightly behind for the M3, with 264hp/tonne against the M4's 266hp/tonne. Accepting the coupe has a slightly favourable centre of gravity and fractional power to weight advantage, in all other respects it's fair to consider impressions of the car's character as interchangeable between M4 and M3.
Which is a long way of saying, yes, this is a reasonable head to head, further enlightened with previous experience of both BMWs and the C63 on their respective launches at Portimao, plus road tests here in the UK.
The difference in character, traditions and mindset of these two cars is obvious from the first push of the starter button. Where the BMW growls away with an urgent, metallic sounding gargle the C63 is pure AMG; a clap of V8 thunder and then a menacing, bassy burble that'll rattle the windows the length of your street. As fluids warm and exhaust flaps close both settle down to a quieter tickover as you pull away. But those first 60 seconds or so tell you a lot about what each car has in store for you.
OK, it weighs another 95kg against a comparable M DCT M3 saloon and 118kg more than this M4, with both BMWs available as manuals weighing 40kg less still. But none of these cars can be considered light and (marginally) by the numbers and (decisively) by the seat of the pants the AMG feels the more potent and muscular car.
M178 engine was reverent attention as we were played a succession of recorded Affalterbach V8s, culminating in the new 'hot-V' twin-turbo motor. And from that first fire-up and every mile that follows that bass is always there, tingling through the car, pulsating in your chest and scoring your every move. For sure, the sound has been engineered. But more naturally than the BMW and entertaining whether you're pottering around town at 20mph or flat out on a favourite B-road.
Only you won't be. Because flat out in the C63 is not somewhere you'll get to experience too often. It's a common refrain with modern performance cars but the C63's abilities so far outstrip any notional sense of what's achievable on the public road as to leave low-speed burbling your only option for enjoying the car. In the previous C63 this was offset by a rawness and response that engaged throughout the speed spectrum. But the new C63 is a much more grown-up and mature vehicle; plusher, grippier, more opulent and perhaps a bit more Mercedes than it is AMG.
Now that huge power is delivered in partnership with all the other systems, meaning you have to be surprisingly lead-footed before any meaningful sense of rear-driven influence kicks in. In engine size and driving style no longer does it feel as over-endowed as the old one. Light steering only adds to this sense of disconnection. Initial softness in the throttle as the turbos spool up doesn't help, though the AMG's extra cylinders and capacity blurs the transition between on and off boost better than the BMW's six. The AMG's steel brakes are slightly easier to modulate than the BMW's expensive optional ceramics; Merc offers the same as an option but for road use they're more than up to the job.
Both downsized, both newly turbocharged, both facing an uphill struggle to win over long-time fans ... arguably this is the first time M and AMG have converged on similar ground after generations of cars built to very clear and different templates. Indeed, having out as a homologation special built to battle Mercedes on the track, the M3 has over generations got closer to the AMG template as it's gained cylinders, weight, complexity and size. And here we are, both brands now offering forced induction, multi-configurable driver modes aplenty, all the latest gadgets and tech and a broader than ever operating window.
the M3 saloon we tested last year the BMW is a feistier, more aggressive machine.
When you look at the baseline figures of the respective entry models the BMW's power deficit does look a little worrying though, the 431hp M3 costing £56,595 against £60,060 for the 476hp non-S C63 saloon. Factor in the M DCT dual-clutch to put it on equal terms with the Merc's seven-speed 'MCT' auto and this narrows to £59,240 though. As tested the initially more expensive sounding Mercedes again narrows the gap, this fully-specced 510hp S saloon costing £73,020 against our M4's £73,870. Ultimately both are expensive cars with many and varied ways to make them more so; prospective owners would do well to spend time on the configurators and cost up each to their desired spec before deciding which ultimately represents better value.
Remember that point about the noise? The BMW backs up this first impression every step of the way by being far more aggressive and pointy than the AMG. You can read more about impressions of the engine's character in the PH Fleet reports but that initial spike of boost dominates the power delivery and the way the chassis puts it to the road. And if you can successfully mitigate the destabilising effect of the turbos spooling up the M engine has a broader and more rev-happy operating window than the AMG V8. If only it sounded better doing so, the artificial blare never convincing yet always intrusive.
Unlike the C63, you're never in any doubt about where the power is going either. The diff locks up far more aggressively, the rear axle always wants to dominate the proceedings and though the variable rack steering is a bit mushy off-centre the front-end dives assertively for the apex, meaning the rear is never far behind. Or ready to overtake. We've said it many times before but this turbo M car has the potential to be a serious handful, which may or may not be to your liking. Contrived or otherwise, this is the more hardcore car by a long shot.
Traditionalists will prefer the older versions of both of these cars. These new ones are almost caricatures, using gizmos and configurability to deliver a digitally enhanced impression of what went before. With a better CO2 figure.
It's a close one too. The Mercedes is way more charismatic thanks to that engine and it's generally warmer demeanour. The damping is way more sophisticated and nuanced than the BMW's too and it's a nicer place to rack up the miles, with the appealing option of an estate if that's your bag. And those huge reserves of power and torque are enough to silence pretty much any protest, including what seems like an initially higher price. Objectively it's probably the better car and more able to slip under the radar when required.
MERCEDES-AMG C63/C63 S SALOON
Engine: 3,982cc twin-turbo V8
Transmission: 7-speed auto with lock-up clutch (MCT), rear-wheel drive
Power (hp): 476@5,500rpm/510@5,500rpm
Torque (lb ft): 479@1,750-4,500rpm/516@1,750-4,500rpm
Top speed: 155mph (limited)
Weight: 1,715kg/1,730kg (EU, with driver)
MPG: 34.5mpg (NEDC combined)
Price: £59,795/£66,550 (C63 S Saloon as tested £73,020 comprising Premium Package interior with Artico leather dash, Nappa leather look door linings, Keyless-Go with keyless entry/start and powered bootlid, Burmester surround sound system, LED Intelligent Light System and panoramic electric sunroof £2,595; Driving Assistance Package with Blind Spot Assist, Distronic Plus cruise control, Lane Keeping Assist and Pre-Safe £1,495; Brilliant Blue paint £646 and 19-inch AMG forged wheels in black £1,735)
Engine: 2,979cc 6-cyl twin-turbo
Transmission: 6-speed manual/7-speed dual-clutch auto (M DCT), rear-wheel drive
Power (hp): 431@5,500rpm
Torque (lb ft): 406@1,850-5,500rpm
0-62mph: 4.3 sec (4.1 sec M DCT)
Top speed: 155mph (limited)
Weight (M3): 1,595kg (1,635kg M DCT, both EU, with driver)
Weight (M4): 1,572kg (1,612kg M DCT, both EU with driver)
MPG: 32.1mpg (34mpg M DCT, both NEDC combined)
CO2: 204g/km (194g/km M DCT)
Price (M3): £56,595 (£59,240 with M DCT)
Price (M4): £57,055 (£59,700 with M DCT, M4 Coupe as tested £73,870 comprising £1,330 for Black Merino leather, £545 for advanced parking package, £2,645 for M DCT transmission, £6,250 for carbon ceramic brakes, £175 for 19-inch M Double-spoke style 437M alloy wheels/Black with mixed tyres, £265 for sun protection glass, £155 for extended storage, £140 for sliding front armrest, £440 for lane change warning system, £395 for Carbon Fibre interior trim, £1,600 for Adaptive LED headlights, £370 for driving assistant, £500 for surround view, £825 for M Head-up display, £675 Harman/Kardon Loudspeaker system, £95 internet and £190 for online entertainment)
C63 vs. M4 pics: Chris Teagles