Mercedes-Benz B 55

What is it?

The B 55 is not a regular Mercedes-Benz model. Nor is it being considered for sale – not now or at any time in the future. Sadly, I should add. Because this wild take on the otherwise wholesomely conservative B-class, created by a team of trainees at Mercedes' Rastatt factory in Germany, is an absolute riot.

As its name suggests, the superbly constructed one-off prototype is well removed from the standard B-class. Having started off life as a humble B 200 CDI, it has been liberated from its standard turbocharged 2.0-litre four-cylinder diesel engine. Shoehorned into its place and other areas of the engine bay is Mercedes’ recently superseded 5.5-litre petrol V8 packing an added 243bhp at 383bhp and 170lb ft more torque at 391lb ft.

Read our review on the Mercedes-Benz B-Class small MPV

What's it like?

Just how the new engine fits under the heavily sloping bonnet and within the tight confines of the compact MPV using the original mounts and without any modification to the standard steel body structure remains somewhat of a mystery, but with polished chrome inlet plumbing and other visual tweaks, it certainly looks the goods.

It sounds it, too. Turn the key and you’re treated to a deliciously throaty soundtrack thanks to a new exhaust system created from various replacement parts that does without the usual silencers and back-pressure reducing trickery. If you didn't know, you could be forgiven for thinking it was the product of AMG, which apparently had no direct input into the new car.

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.