The engine is not the only highlight. Mercedes' trainees have also ditched the B-class's front-wheel drive layout for rear-wheel drive, running a propshaft from its new seven-speed automatic gearbox under the flat floor towards the rear where it mates with an axle from the old E 430 Estate; Its 1540mm rear track allowed them to retain standard rear bodywork but required new pick-up points for the rear multi-link suspension and a smaller fuel tank.
To cope with the increased performance, it also adopts the brakes from the decade-old C 32 AMG with 345mm discs up front and 300mm at the rear. Because of the limited development, though, there's no traction control or stability program to corral the engine's reserves.
The result is a driving experience quite unlike any other B-class – unlike any other Mercedes, for that matter. Without registration for road use, we used the Rastatt test track to determine the B 55 is more than mere show. It also possesses surprisingly mature dynamic properties.
With an extra 15kg placed over the front axle compared to the B 200 CDI, weight distribution definitely favours the front end. But there is sufficient balance and grip to allow you to attack corners with real gusto. Apart from a lack of self-centring with the steering, whose packaging has been compromised by the need to give up so much space to the engine and thus runs a smaller hydraulic pump than is perhaps required, the B55 also steers accurately, rides with impressive comfort and is free of any obvious vices.
With a kerb weight of 1620 – 180kg more than the B 200 CDI – it is decently quick in a straight line. Andreas Wurz, a foreman in the technical vocation training department at Rastatt largely credited with the idea behind the new car, reckons it should be good for 0-62mph in under six seconds when he finally gets around to strapping some measuring equipment to it. He's lying, of course. This thing will easily run in the low five-second bracket.
The B55 looks rather striking for what is essentially a high-powered MPV. As you can see, Mercedes' team of trainees managed to package the new engine and driveline without any obvious changes to the standard B-class body – a remarkable achievement given the major driveline modifications that have taken place underneath. But with a lowered ride height and 18-inch wheels – 8 inches wide up front and 9 inches at the rear, shod with 235/40 (front) and 255/35 (rear) profile tyres and two centrally mounted chrome tailpipes it possesses a much more aggressive stance than its standard sibling.
Should I buy one?
Sadly, though, it'll never progress beyond this prototype. But with a new, second-generation B-class due out at the Frankfurt motor show in September, it is a fitting way to send off the first-generation of Mercedes' popular compact MPV.
Mercedes-Benz B 55
Price: na; Top speed: 155mph (limited); 0-62mph: 5.2sec (est); Economy: na; CO2: na; Kerb weight: 1620kg; Engine: V8, 5461cc, petrol; Power: 383bhp at 6000rpm; Torque: 391lb ft at 2800rpm; Gearbox: 7-spd automatic