Comprex-charged baby 'AMG' to take on RS3 and M1

AMG's recent power surge is about to continue in smaller cars, with a hammer-time forced-induction V6 set to take on models like Audi's upcoming RS3 and BMW's crunching, twin-turbo M1. But rather than turbo or conventional supercharging, the new powerplant will revive the Comprex supercharger.

Still buzzed by the critical success of its SLS supercar, Mercedes-Benz's hot-rod division is about to aim straight at younger customers with an all-wheel drive sedan based around the upcoming new-generation B-Class Mercedes architecture.

Parent company, Mercedes-Benz, previewed the look of the new AMG's donor car with its F800 at the Geneva Motor Show, and the production car, code-named C117 EVO, will give AMG a €35,000 price point to make it far more accessible than the current entry level C63. Already being dubbed a CLS-lite, the new car will be around 4500mm in length (around 400mm shorter than its bigger brother) but it will share its philosophy of frameless doors and four-door coupe styling.

And it will render bigger shocks than just its styling.

Mercedes will debut its new twin turbo V6 engine, dubbed M276, complete with four-valves per cylinder and direct fuel-injection, in the CLS350 later this year. While the baby AMG will also use a smaller, 3.2-litre version of the M276's basic layout, sources have confirmed AMG has tossed out Benz's turbochargers in favour of the relatively untried Comprex forced-induction system.

The technology, which is already said to be developing in excess of 300kW from the V6 in testing (but will settle at around 295kW in production trim), will make AMG the first car company in the modern era to develop the old, but rarely-used forced-induction system, which effectively combines characteristics of both turbo and supercharging systems.

"There are some rumours around it (comprex) even here in Switzerland," Dr Leopold Mikulic, Mercedes-Benz's Vice-President of Powertrain Development told the Carsales Network.

"Comprex has no turbo lag, though, because it operates on a very different principle. This technology comes back now with a new approach, which could be a viable competition to turbocharging. It has to prove itself in high volume first. We will see about it for our V6."

The stunning admission means AMG will use the technology, which uses a combination of a belt driven turbine and exhaust pulse energy to directly force feed the engine, in production as soon 2013.

The system is technically known as a supercharger, because it is belt driven but that's where the similarities end.

Invented in 1987 by Swiss engineering firm, Brown, Boveri and Cie, the Comprex system is said to boost power by up to 30 per cent by additionally directing the energy from the exhaust manifold's pulses into a chamber, where it directly acts on incoming air to force it into the inlet manifolds.

AMG would not be the first car company to use it in production (Mazda, no strangers to quirky engine technology, sold more than 150,000 Comprex Diesels, though none remain in production), but it will cast new light on the modern need for forced induction engines.

"The creators of Comprex were pushing this type of technology many years ago," Dr Mikulic said. "There was too much competition for it 25 years ago; there was superchargers and competition with turbochargers.

"There was no variety with it and they had a lot of problems. And you had to design it from new with every car, because it could not be made in a modular unit."

Using Comprex will give AMG not only a power and fuel economy boost, but will help position the brand as a technology leader, not just a tuner of fast Mercedes-Benz donor cars. That will be welcome in this class, and AMG plans to market it heavily as the high-tech player in the class, especially when it is mated to a seven-speed double-clutch gearbox and the latest Haldex all-wheel drive system.

Outgoing AMG boss Volker Mornhinweg confirmed as much in a pre-Geneva Auto Salon interview, saying AMG's compact car "will have a premium of both power and torque over anything from Audi or anything planned by BMW."

Said Mornhinweg: "Our step into the compact class will not only have an impact with average consumption, but it opens us up to a new group of customers. We are reinventing ourselves while remaining true to our values."

Sources inside AMG confirmed they've had a flood of benchmarking cars through the Affalterbach factory as they try to get to grips with what's expected from the competition. AMG engineers have been busy driving the Audi S3, the Focus RS and hot versions of everything from Renault's Megane to Honda's Integra.

But while AMG is capturing the headlines with its new Comprex technology, Mercedes-Benz itself is about to launch a new range of engines.

Criticised in some quarters for a lack of refinement in its current powertrain line-up, Mercedes will soon launch its MoVe engine range which promises up to 25 per cent lower fuel consumption and more power.

The new MoVe marketing tag will cover Benz's new V6 and V8 petrol engines, with both powerplants moving towards turbocharging, lower revs, lower consumption and more power.

A 3.5-litre V6 will boast 225kW when it debuts in this year's new CLS, while the V8 in the CLS will shrink to just 4.6 litres, though it will produce 320kW.

Benz is counting on the adoption of stratified, direct fuel-injection and four-valve cylinder-heads to modernise the range, even though the basic engine blocks will keep their 90-degree vees and remain otherwise similar to the outgoing engines.

Code-named the M276 (V6) and M278 (V8), the engines will also spawn forced induction versions.

Says Mikulic, turbo-charging is the "only option for sustainable engines" for cars from the C-Class all the way up to the S-Class.

"The V8 is still a good base engine but we should add some new technologies to it, like direct-injection and turbo charging," he said.

"That combination gives us viability in fuel economy and consumption and the reduction in displacement gives a very nice package.

"We can do all the work on the chassis, but for fuel economy, we come to back to the engine and downsizing and down-speeding are the way forward.

"That means low-end torque engines and that means turbo charging. No other way around it," he said.

Here's a useful link to explain Comprex supercharging.

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