Mercedes-Benz B 55 (2011)

The Mercedes-Benz B 55 is a one-off, factory-sanctioned skunkworks project that turned a humble, front-wheel-drive B-Class (W245) into a rear-drive hot hatch with a naturally aspirated 5.5-liter V8. Conceived as a training and showcase exercise at Mercedes-Benz’s Rastatt plant, the B 55 transplanted the M273 V8 (about 388 hp and 530 Nm) and 7G-Tronic automatic into the compact MPV’s shell, added a rear-drive axle, and re-engineered brakes and suspension to match. The result was equal parts pedagogy and provocation: a perfectly ordinary white B-Class that idled like a muscle car and accelerated like a junior AMG, built by apprentices under master-technician supervision with support from group engineering.

History

The project’s spark came from Rastatt plant manager Peter Wesp, who challenged the site’s training workshop to create “something special” that would stretch apprentices beyond routine service tasks. The donor was a B 200 CDI already assigned to the training department. Under the lead of training master Andreas Würz, the team completely stripped the car and mapped a conversion path that would demonstrate real-world integration: powertrain, driveline, electronics, cooling, chassis geometry, NVH, and legal lighting—all within a tight calendar.

Micro-dates anchor the story. Public reporting in December 2010 first revealed the car’s existence, describing an eight-month build led by Würz. In early January 2011, Mercedes released photos and details to media and enthusiasts, and a short factory video walked viewers through the conversion at the Rastatt training hall. Contemporary write-ups and image sets landed on enthusiast outlets within days, framing the B 55 as both a stunt and a serious learning exercise. Although it never appeared as a formal motor-show concept, it toured the media circuit as a working prototype—a drivable, fully finished B-Class with a hand-built personality and factory-grade workmanship.

Design Features

Drivetrain Re-architecture

The B-Class’s sandwich-floor layout and transverse engine bay made a V8 swap non-trivial. The team sourced a 5.5-liter M273 V8 (rated around 285 kW/388 hp and 530 Nm) with its 7G-Tronic control unit and wiring. To avoid torque-steer absurdity, they abandoned front-drive and converted the car to rear-wheel drive, installing a rear axle from a W210 E-Class. A new rear subframe and mounting structure were fabricated to package the differential and to carry the loads the B-Class floor was never designed to see. The propshaft was selected to fit with minimal surgery, but hard-points, exhaust routing, and heat shielding were re-engineered for durability and clearance.

Chassis, Brakes, and Rolling Stock

Power without control would have been a poor lesson. The B 55 received KW coil-over suspension, as much to tune ride height and corner weights as to sharpen transient response. Braking came from C 32 AMG hardware—large ventilated discs and multi-piston calipers—chosen for parts availability and proven thermal capacity on a car of similar mass. Unsprung gear was finished with AMG five-spoke alloys—8.5×18 inches front and 9×18 inches rear—wearing performance tires that filled the arches and stabilized the stance.

Packaging and Systems Integration

The engine management and transmission ECU were transplanted as a set, then adapted to the B-Class body network. Cooling circuits were reworked with higher-capacity radiators and rerouted hoses to suit the new longitudinal layout. The exhaust used compact catalysts and a twin-pipe arrangement that exited discreetly, preserving the B-Class’s sleeper aesthetic while flowing enough for a 6,000-rpm V8. Under-hood heat soak—always a risk in tight conversions—was managed with shielding and the V-engine’s factory thermal cladding.

Exterior and Cabin

Deliberate restraint defined the look. The car remained visually close to a stock W245: white paint, standard body panels, subtle ride-height drop, and AMG wheels. No flares, no wings, no wide-body narrative—because the brief was to demonstrate engineering, not to advertise it. Inside, the cabin kept the B-Class ergonomics and controls with minor trim tweaks; the fascinating parts were hidden: the re-pinned looms, the harness integration, and the extra cooling and driveline controllers tucked into factory-style locations.

Learning Objectives (Human Touch)

As a training program, the B 55 forced apprentices to engage with systems thinking: how an ECU handshake affects instrument-cluster behavior; how prop-shaft angles influence vibration; how brake bias changes with axle-weight shifts; how to validate bump-stop clearance on a lowered car with a heavier front end; how to keep NVH civilized when the cabin sits close to a big-bore V8. That is why Mercedes later used the B 55 in a video feature—less as a halo oddity and more as a case study in method, documentation, and cross-disciplinary collaboration.

Specifications

Property	Value
Base vehicle	Mercedes-Benz B-Class W245 (donor: B 200 CDI)
Engine	M273 5.5-liter V8, NA (E55 variant)
Output (factory rating)	≈388 hp (285 kW) @ ~6000 rpm
Torque (factory rating)	≈530 Nm (391 lb-ft)
Transmission	7G-Tronic 7-speed automatic
Drivetrain	Rear-wheel drive (conversion)
Rear axle	From W210 E-Class (bespoke subframe/mounts)
Brakes	C32 AMG front/rear hardware
Suspension	KW coil-over system
Wheels	AMG 8.5×18 (front) / 9×18 (rear)
Claimed performance*	0–100 km/h ≈ 5.2 s; top speed ≈ 270 km/h (prototype figures reported in period press)
Curb mass	Not publicly certified; significantly higher front axle load vs. stock; balanced by rear-drive conversion

*Performance numbers circulated in contemporary German reporting from the project team; no type-approval tests were published.

Production Status

Concept → Production (what carried, what died).

Carried (spirit): The B 55 validated a corporate culture where apprentice projects can tackle genuine systems integration, not just cosmetic builds. It also presaged the brand’s later acceptance that compact cars could credibly carry high-output powertrains—even if Mercedes-AMG went the turbo-four + AWD route in the A 45/CLA 45 era rather than shoehorning large NA V8s.
Carried (parts logic): The use of existing Mercedes modules—engine, gearbox, rear axle, braking—demonstrated how platform commonality can enable radical one-offs without exotic fabrication.
Dropped: There was never a production B-Class V8 or a “B 55 AMG.” The conversion remained a single prototype. The rear-drive layout, the M273 V8, and the AMG brake package were pedagogical choices, not homologation steps.
Timeline notes: Public reveal and factory video coverage clustered around Dec 2010–Feb 2011; images and details originated from Rastatt communications and were syndicated by automotive outlets worldwide. The car has occasionally resurfaced in “forgotten one-offs” features and brand-heritage content.

Design genealogy and authorship.
Authorship is credited to the Rastatt plant training workshop under Andreas Würz, executing a brief set by Peter Wesp. Upstream, the drivetrain and driveline donors sit within the S-/E-/C-Class parts bin of the 2000s. Downstream, the B 55 lives mostly as a reference point in enthusiast culture: the ultimate sleeper B-Class, a “what-if” that underscores how robust Mercedes modules can be when recombined by competent hands.

Sources

Autoevolution — “Mercedes B 55 with V8 Engine and 388 HP Presented” (Feb 2, 2011). https://www.autoevolution.com/news/mercedes-b-55-with-v8-engine-and-388-hp-presented-gallery-30565.html
NetCarShow — “Mercedes-Benz B55 Concept (2011)” (factory photo set and summary, 388 hp/530 Nm, 7G-Tronic, W210 axle, C32 brakes, KW suspension). https://www.netcarshow.com/mercedes-benz/2011-b55_concept/
paultan.org — “Mercedes-Benz B 55 – 388 hp V8 and rear-wheel drive!” (Jan 3, 2011). https://paultan.org/2011/01/03/mercedes-benz-b-55-388-hp-and-rear-wheel-drive/
Car Enthusiast — news brief (Rastatt trainees; Wesp; one-off; Dec 2010/Jan 2011 coverage). https://www.carenthusiast.com/news.html?id=5274&mode=article
Welt (Die Welt) — feature with micro-claims (eight-month build; 0–100 km/h ≈5.2 s, ≈270 km/h; Dec 17, 2010). https://www.welt.de/103887567
MotorAuthority — “Apprentices build one-off Mercedes-Benz B55 hot hatch / Creates one-off 388-hp V-8 B-Class” (Dec 21, 2010; Feb 1, 2011). https://www.motorauthority.com/news/1052746_apprentices-build-one-off-mercedes-benz-b55-hot-hatch ; https://www.motorauthority.com/news/1054667_mercedes-benz-creates-one-off-388-hp-v-8-b-class
Wikipedia — “Mercedes-Benz M273 engine” (E55 5.5-liter output references). https://en.wikipedia.org/wiki/Mercedes-Benz_M273_engine
CarThrottle — “Cars You Forgot About: The One-Off Mercedes B55 V8” (retrospective; W210 axle note; Apr 18, 2025). https://www.carthrottle.com/news/cars-you-forgot-about-one-mercedes-b55-v8

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