Mercedes-Benz AMG GT vs BMW Alpina B4

What's the difference?

This is no Lotus, but damn if it ain't a hell of a good time, and proof positive that electrification can enhance the V8 experience, rather than ruin it.

You could almost call the B4 S the anti-M4. It's still fast and practical but from a completely different perspective. It's much more a grand tourer than the M4 and even with the Akrapovic exhaust (usually a byword for joyous, anti-social racket), subtle.

For some, the price won't matter because the Alpina delivers what they want - M4-like straight line performance without the histrionics or the uncompromising chassis. And there's also a bit of that perverse exclusivity of the styling that you won't get anywhere else.

It's a mean, but somehow still sleek, looking beast, this big AMG, but it's also immediately recognisable as a thing of intent.

Up front, there's the huge vertical-slat grille that looks like it drove straight out of a Stephen King novel, a massively domed bonnet, and these vacuum-like side intakes that look like they could suck in stray animals.

Then, at the back, there are twin dual-pipe exits (for four in total), and an automatic wing that pops out of the rear bodywork. And all of that's capped off with these massive 21-inch forged alloy wheels hiding golden ceramic-composite brakes.

Mean, yes, but not quite as aggressive as you might expect the most powerful AMG to date to come across, perhaps.

Inside, it's more subdued again, with the AMG presenting a pretty passenger-friendly space, with all the Benz tech you'd imagine, including the massive screens, and — thanks to its air suspension and drive modes — the ability to tailor the ride to your liking, meaning a comfortable and premium experience, despite the power under your right foot.

Alpina has always had a particular aesthetic that could uncharitably be termed as mid-'80s West German - all set square angles and body graphics. Think David Hasselhoff's Berlin Wall look. The company has never really deviated from adding squared-off body bits to the various BMWs it has rebadged under its long-running agreement.

For the B4S, Alpina adds the signature billion-spoke alloy wheels (only a slight exaggeration), a new front splitter complete with Alpina lettering, a weirdly proportioned boot lid lip spoiler and - not even joking - pinstripes. Like I said, mid-'80s West German. You can still recognise the sleek 4 Series Coupe but perhaps the worst of it is the super-sized, wonky-looking ALPINA B4S on the boot.

Inside is rather more restrained apart from the ill-fitting Alpina plaque under the climate control. Again, it's all 4 Series in here, with the lovely Merino leather liberally applied across the cabin. Less lovely is the wood on the door pulls and console but the door cards have an oddly appealing woven leather which looks and feels good.

Sadly the standard 4 Series steering wheel is along for the ride. There's nothing wrong with it - although the Alpina logo does look out of place - but if I were a product planner, I'd beg for the lovelier M wheel.

It's not overly practical, given its size, with AMG locking in a four-seat configuration with a fixed rear pew that limits boot space. You can get folding seats, but only as part of an option package.

What you're left with is a vehicle that stretches 5054mm in length, 1953mm in width and 1447mm in height, but that serves up rear seating for only two – albeit very comfortably – and, because of the electric battery and motor being housed at the rear, boot space of just 335 litres.

There is triple-zone climate control, and the rear seating is lounge-like and luxurious, while the up-front space is ample for two full-size riders, too.

There's no spare, with AMG's 'Tirefit' puncture repair system on board.

If you're in the front, you're in luck - it's a comfortable place to be, with plenty of leg and headroom. Down back isn't terrible despite the coupe roofline. The two seats are nicely shaped for maximum comfort and separated by an odd plastic tray. The fold-down armrest has two cupholders.

Front seat passengers score a pair of cupholders (bring the total to four for the car) and the long doors will hold a bottle each.

The boot swallows a reasonable 445 litres, which isn't at all bad.

If you thought BMW don't mess about when pricing up its cars, you best strap yourself in. The 440i-based B4S starts at a solid $149,900. That's $48,000 more than the 440i and significantly more than an M4 Pure. But there's plenty of gear on offer and some genuine, bespoke Alpina additions.

Standard are 20-inch signature Alpina alloys, 16-speaker harmon kardon-branded stereo with DAB, super-soft Merino leather everywhere, dual-zone climate control, around-view cameras, reversing camera, sat nav, keyless entry and start, front and rear parking sensors, active cruise control, heated and electric front seats, head-up display, auto headlights and active LED headlights, LED taillights and electric sunroof.

The stereo and sat nav are run by BMW's iDrive. It's a cracker of a system and almost gets away without Apple CarPlay and Android Auto. The absence of such simple pleasures at this price point is a bit lame, but here we are.

It's not just what's under the bonnet, but what's at the rear axle, too.

But let's start at the front, shall we? Here, a familiar twin-turbo V8 engine lurks, producing a potent 470kW and 900Nm, which is fed through a nine-speed automatic, complete with paddle shifters and several drive modes, including the traction-limiting 'Race'.

But that is then joined at the rear by an electric motor with its own two-speed transmission, and which produces 70kW and 320Nm – or up to 150kW for 10-second blasts under heavy acceleration.

Combine both, and you're tapping into around 620kW and in excess of 1000Nm, enabling a sprint to 100km/h in just 2.9 seconds, and a flying top speed of 316km/h.

A lot of your extra money turns up under the bonnet. These days the 440i packs BMW's slick B58 turbo straight six and the B4S does likewise. The boys from Buchloe in Bavaria (there are certain to be women there, too, I just liked the alliteration) added a pair of Alpina-spec turbos to generate a whopping 324kW and, more importantly, 660Nm. Alpina says 600Nm (the max torque figure of the brilliant M4 CS) is available from 2000-5000rpm, while the full 660Nm is available from 3000 to 4500rpm.

The M4 Pure has 317kW and 550Nm from the S55 straight-six. Just so you know.

Like the 440i but unlike the M4, the B4S employs the dependably brilliant eight-speed ZF automatic found throughout the BMW range.

Fuel efficiency is surprisingly impressive for a vehicle this big and powerful, with Mercedes claiming 7.7L/100km and 175g/km of CO2 on the combined cycle.

Helping that is a the 6.1kW battery, which delivers just 12km in all-electric driving range, but helps reduce overall fuel use.

This AMG is AC power only, meaning you can't recharge using fast chargers, but the brand says its secret trick is its ability to recharge itself using captured kinetic energy incredibly quickly – largely negating the need to plug in unless you want to unlock that EV range – with Merc suggesting that, on a race track for example, the battery will discharge and charge itself continuously as you're lapping.

Alpina quotes 7.9L/100km on the combined cycle and we went through the premium unleaded at the rate of 11.7L/100km. I enjoyed myself, so that's not a terrible result.

There's a lot of big numbers surrounding the Mercedes-AMG GT63S E Performance, but let me throw another one at you – 245km/h.

That was the high score I saw pop up on its digital speedo as the big and electrified Mercedes flew down the main straight at Sydney Motorsport Park (formerly Eastern Creek), before my courage ran out and my foot found the brake.

That kind of velocity is mind-bending in a vehicle this big, and so is the way that power is delivered, with the AMG's big brain deciding how and when to maximise power from the engine and electric motor to deliver a constant surge of torque that shoves you back, and the GT63S E Performance into the future.

But big acceleration is hardly surprising with that much power. What is a little more impressive is how easy this four-door supercar is to wrestle around a racetrack.

Sure, the feeling-out process is a little more involved, as you figure out how and when you'll feel the weight shifting, and as your brain struggles to compute how what's happening is even possible, but after a couple of laps the AMG settles into an easy, flowing rhythm that, while never feeling light on its feet, also doesn't feels like you're piloting a bus.

At least part of that is down to the wizardry on board, like the 'AMG Air Suspension', the rear-axle steering and the limited-slip diff, all of which combine to make the GT63S feel tighter and sharper than it would otherwise.

But it's also partly down to the prodigious power on offer – perfect corner entry and exits are less relevant when you have a cruise missile strapped to your right foot that doesn't just quickly make up for any driver errors, but shrinks the space between corners to the blink of an eye.

Yes, it's heavy, and there isn't much that's pure about the go-fast experience, but it left an ear-to-ear grin on my face, and isn't that priority one for any new AMG?

How does it drive on the road? That I don't know, as this was a track-only drive day. But we will get one on a proper test soon and let you know.

One of the key differences between the B4 and M4 is the ride. While the M4 can crash over bumps and generally be a little hard to live with, the crew in Buchloe have gone after a much more plush ride. And in that they have succeeded because the B4 S is a mighty fine cruiser. Bumps are dismissed with a haughty disdain, even Sport + silliness doesn't completely write-off ride quality.

Very impressive too, is the steering. While still not at Lotus Elise levels of feel (few cars are), the Alpina tweaks connect the your palms to the road with more clarity than what you'll find in the 440i or M4. Where the M4 particularly adds too much weight, the 440i is a bit more circumspect in that regard.

And then we come to the engine. The B58 six is a belter, better even than the N55 that preceded it. It's still a 3.0-litre straight six but is part of BMW's modular engine family that starts with a 1.5-litre triple in the Mini and 1 Series. The Alpina-spec turbos are noisier, the Akrapovic exhaust lighter and also noisier. It doesn't have the all-out crackle and pop of an Audi or Merc (perish the thought), but when you're on it, the B4 means business. The 660Nm of torque, available over a wide rev range, delivers a steel fist wrapped in a velvet glove and bubble wrap - the speed builds rapidly but smoothly. 

The approach to the chassis tune seems to be based on the driving talents of mere mortals on normal roads, which is kind of like the 440i. It's terrific fun to drive hard but it's very forgiving and patient. The great thing about it is that you wouldn't think twice about jumping in it for the long haul, so comfortable and quiet is the cabin. The M4 will leave it for dead on a winding road, but that's perfectly fine.

One irritant is the replacement of the admittedly cheap BMW gearshift paddles with weirdly non-tactile buttons. They're not particularly easy to use and, probably worse for a sporty car, unsatisfying. It's an odd detail with which to go off the reservation. Cheeringly, the eight-speed ZF is its usual perfect self, so you don't have to worry too much about manual mode or go old school and use the shifter.

The Alpina ships with six airbags, ABS, stability and traction controls, ABS, stability and traction controls, forward collision warning, forward AEB, road sign recognition and active cruise control.

There are also two ISOFIX points in the rear. Neither the Alpina nor the 4 Series has an ANCAP safety rating.

The GT63S E Performance is covered by Mercedes' five-year, unlimited-kilometre warranty, and you can pre-pay your service costs to keep the prices down.

Service pricing for the electrified model is yet to be confirmed.

Alpina offers a two-year/unlimited-kilometre warranty which is a bit behind the times and not in keeping with the price point. Servicing is another matter altogether and you're subject to your dealer's standard charges for servicing.