German marques building four-cylinder engines

The times, they are a'changin', and it appears no more so than in Germany. With the continuing trend towards more fuel-efficient cars, even performance stalwarts AMG, Porsche and BMW have begun serious work on small, four-cylinder engines to line up beside their boxer sixes, V8s and V10s. But will their smaller offerings be accepted by their performance-oriented clientele?

Here is a rundown of the progress on the four-cylinder engines from AMG, Porsche and BMW.

AMG

The boffins at Mercedes's tuning department are racing against time to perfect their first four-cylinder engine before the launch of the company's baby saloon, based around the next B-Class, in two years.

Technical problems with its radical Hyprex forced-induction system have forced the Benz hotshop to shift its attention to a twin-scroll turbocharging system to crank out AMG-style, rubber-burning power for its small saloon.

Stuffed into a car that will look a lot like last year's Geneva Motor Show concept stunner from Mercedes-Benz, the turbo four pot will blast to 100kph in under five seconds.

"If we make it fast enough with the right sound, traditional AMG buyers won't worry too much that it's only four cylinders," AMG boss, Ola Kaellenius, insisted.

Yet AMG is refusing to abandon the controversial Hyprex system, despite two major development headaches.

"We have to really, really hurry with this twin-scroll turbo now, though," AMG R&D boss, Freidrich Eichner, said.

"But we have a parallel programme running with Hyprex, so we will continue to develop it, but now we won't have it in production before 2013.

"We will make it work, though, because the problems are not insurmountable and we are convinced there are enormous benefits."

Hyprex is a development of the original Comprex concept, which was belt driven off the crankshaft and used exhaust-pressure pulses to force air into the inlet chamber, creating a more-powerful and cleaner combustion process.

AMG rejected the idea of the Comprex unit's mechanical losses and, instead, uses an 800W electric motor to drive its Hyprex unit, which is basically a canister that redirects pulses of exhaust pressure to force feed air into the engine.

But AMG insiders have said development is being held up by two problems.

"The first is when the catalyst temperature goes under 600 degrees, it does not work properly and creates too many emissions," our source said.

"The second is that if the exhaust gases mix with the fresh air in the exhaust, then there is a bang and the Hyprex is not working anymore."

Porsche

The Stuttgart-based company's outgoing R&D boss has confirmed the German sports car maker will launch a four-cylinder engine before the end of next year - and it could find its way into the legendary 911 and a new, sub-Cayman Porsche.

On his way to head up Volkswagen Group brands Bugatti and Bentley, Wolfgang Durheimer suggested the new engine would be powerful enough for the Boxster and Cayman twins, but would save "eight to 12 per cent" in fuel consumption.

"We have a four-cylinder boxer engine under development," Durheimer confirmed to journalists at the Detroit motor show, "And it can be applied to the Boxster and the Cayman."

Durheimer said the new 2.5L, four-cylinder engine will be based on the architecture of the existing six-cylinder range used in the mid-engined Porsches.

Pointedly, though, he refused to rule out the engine one day being used inside the legendary 911, despite its six-cylinder traditions.

"It also could be applied if necessary to the 911," he says. "Our decision is, on the 911 side, we'll stay with the 911 flat [Porsche's iconic, horizontally opposed six-cylinder engine], but there are opportunities for the future."

Durheimer suggested the engine would be production ready before the end of 2012 and insisted the engine had been completely engineered in-house, with no input from the Volkswagen Group.

"I think a four-cylinder boxer engine in a Porsche sports car is viable as long as the performance level does not suffer. If you are talking about performance you need a turbo," he said.

"These people [our customers] are very successful businessmen, they are public leaders and they don't want to have a bad situation why it has bad consumption or a bad performance level."

What Durheimer didn't say was that the engine would also power Porsche's upcoming sub-Cayman model, built off the VW Group's MRP mid-rear engined aluminium chassis architecture.

This is the same architecture that sat beneath the original Audi R4 e-tron and Volkswagen's BlueSport convertible prototype. While Audi has yet to find a home for an MRP-based car in its coupe-rich line-up, Volkswagen is keen to build the BlueSport.

Durheimer, though, hinted that any other MRP-based car would need to find another engine, insisting it would only ever power Porsche models.

BMW

The luxury brand will fire the first shots in an upcoming prestige four-cylinder engine war when it replaces its classical straight-six with a turbocharged four pot by the middle of this year.

The new petrol engine, dubbed N20, will soon debut in the X1 within weeks before it finds homes in everything from the X3 to the Z4 and even the 5 Series.

Combining direct fuel injection, twin-scroll turbocharging and variable valve timing and lift, the N20 engine will boast 241hp and 350Nm of torque.

While its European debut will be beneath the engine bay of the X1, it will also be strong enough to become the first four-cylinder BMW sold in the United States since the 1998 318i when it arrives in the Z4 SDrive 28i in September.

Having four cylinders won't make it slow, and BMW claims the X1 xDrive 28i will punch to 100kph in 6.1 seconds (or 6.5 with the eight-speed auto) on its way to a 240kph top speed. The lighter Z4 will be even quicker, and BMW sources expect a 0-to-100kph sprint in the low five-second bracket.

It's also more economical than the basic six-pot it replaces, with BMW claiming 7.9L/100km on the combined cycle for an average of 183 grams of CO2/km.

While the 3 Series is an obvious candidate for the N20, BMW is too deep into its model cycle to bother investing in the production engineering for it, so it will have to wait for the next, all-new 3 Series.

For the US, limited production capacity in the X1's Leipzig factory has pushed the X1's arrival out from the scheduled spring date to the last quarter of the year - at the earliest.

Heavily based around the engineering platform of the 3.0L six-cylinder TwinPower engine range, the new engine will, initially, arrive as a 1,997cc with enormous flexibility.

While its peak power will arrive at 5,000rpm, it delivers its peak torque from an incredibly diesel-esque 1,250rpm. It uses an all-aluminium crankcase and a 10:1 compression ratio, combined with a heavily oversquare architecture to generate a 121hp/litre specific power output.