BMW\’s New Four Cylinder: The Details

Apr 26 • E89 Z4 Roadster, EfficientDynamics, Official News, Technology7 Comments

We all know times are a changing; the age of horsepower wars and increasing performance through displacement is a closed chapter in the book of automotive history.Cheap and seemingly endless petroleum based fuels are really not so cheap these days and definitely will be approaching Mad Max like conditions sooner than many had originally thought. Greenhouse gas emissions threaten air quality and whether or not the climate is changing is a debate for another day but as a global society we are trying to get more from less in order to conserve what we do have. All of this has opened the eyes of auto manufactures and consumers, especially BMW through its Efficient Dynamics program and more recently introduced sub brand BMW i. Times have changed so drastically that BMW will now be selling four cylinders in the US again, something that has not occurred since the 1990 ‘s.

The aluminum N20 four cylinder is so advanced and such a marvel it is not even worth comparing it to the previous stateside BMW offering. The N20 will feature a single dual scroll turbo taking gasses from opposing cylinders to force feed the engine air at 10-11 PSI. It produces 240hp and 260 ft/lbs. Staggering, but possible due to a number of key components- direct injection, variable valve timing and lift (VANOS and Valvetronic). It produces a whopping 120 hp per liter! Some of the intricacies that would go unmentioned by most is what we found the most interesting.

In our discussions with Dr. Harald Unger at NYIAS, head of inline engine development in Munich, we developed an excellent feel for these new breakthroughs that make this engine look so good; at least on paper. This engine is the first from BMW that we know of that features LDS (Lichtbogendrahtspritzen) coated cylinder walls. LDS has already been used for a handful of years by other manufacturers (namely Mercedes Benz ‘s AMG division) with great success. LDS is also known as a twin wire arc spray process.A twin wire arc spray gun is composed of two consumable electrodes (two iron wires in BMWs case) brought toward a converging point wherein an electric arc is generated. This arc then melts the continuously advancing iron wires. An atomizing gas (inert) flowing through the arc produces a molten droplet spray jet that is directed toward the surface of the part to be coated, in this case the aluminum cylinder wall. It is basically a plasma cutter/welder that has the molten metal blown with the droplets creating a coating. What LDS permits is a thinner/lighter cylinder wall, for the N20 that is initially .4 mm which is honed down to .2mm; minuscule when compared to the typical iron sleeve. The decreased thickness allows for greater thermal transfer and consistency all while allowing extra cooling channels (part of the water jacket) between cylinder bores so the engine can been tuned “hotter ” since the cooling properties are greater.

Aside from the space age coating, the engineers have tweaked the angles and balance in this engine to make it nearly as smooth at 5k rpms as the inline six it replaces. Unger explained, that NVH is as close to a six as is possible with current technologies but “it ‘s not possible to achieve it completely “.This is accomplished by first offsetting the crank and pistons by 14mm. The next step is to use two height staggered (but inline) balancer shafts which are located in the bottom end/oil pan to harmonically balance the engine as much as possible. The lower shaft also powers a MAP controlled oil pump- this essentially means the engine management software activates a solenoid which allows oil to be pumped through galleys. This pumping is based on engine demand (load/RPM and temperature) and is near instantaneous.To further improve smoothness the engineers used a dual mass fly wheel and centrifugal fly weights. These effectively act like those little weights on your car ‘s wheels, balancing rotation but unlike the wheel weights these are independently adjustable (really great stuff in our opinion).

With a flat torque curve and quicker 0-60 times, customers will feel the car as faster all while consuming 20% less dead dinosaur. Which in these days of $4.50+ premium is not a bad thing for the wallet or the planet. According to Dr. Unger, the 6 speed manual will see almost identical fuel economy numbers as the automatic. This is thanks to changes in gearing which were permitted because of the flat torque curve and quick revving nature of this engine.

So you have read this far and are concerned that we have not mentioned weight; How much does lopping off a few magnesium cylinders save you? A 22 pound loss is netted and that is nothing to sneeze at considering a dual scroll turbo, Valvetronic and some plumbing was added.

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We look forward to testing the N20 engine as soon as we get the opportunity to as it sounds like a sweetheart of an engine and will form the basis of the majority of BMWs future offerings. It will even spawn an ///M version if sources are to be believed.

Our future review will come from behind the wheel of a roadster, the Z4 sDrive28i and not the as planned X1. The X1 was to launch in NY but thanks to the world markets consuming more than BMW can currently produce a US launch has been pushed back indefinitely- the X1 is coming just there is no set timeline currently but the four cylinder engine will be here and will be the base engine in new models for years to come.

Source: R. Bolot, H. Liao, C. Mateus, C. Coddet et al. (unknown). Optimization of a Rotating Twin Wire-Arc Spray Gun. Unpublished White Paper

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  • stefan

    Is anyone else confused at why they are only wringing out 260ft/lb at 11psi???

    • JRobUSC

      no, since it’s producing the maximum 260lb-ft from 1250-4500RPM. That torque plateau is much more useful for day to day street driving than a higher maximum figure. They could certainly tune it for more power (like an Evo or WRX) but then it would be peakier and much more laggy at low RPM (again, like an Evo or WRX). That type of power delivery wouldn’t make much sense in a base model X1, X3, 5-Series, etc., though I wouldn’t be surprised to see BMW do it with an M version of the engine.

  • Adam

    Very creative little motor, and knowing BMW it’s probably very flexible and could be tuned and adapted to many vehicles. I imagine that since this engine is to serve as a basis for other BMW engines we can sort of figure what bigger engines will be like for power and consumption. Now if M creates a variant of this… I’ll be hooked. Four cylinder engines are nothing new or exciting so for this one to have the enthusiasm it does really says something.

  • Millerformula1

    With the new and ever demanding CAFE reqiirements, the N20 engine is “cutting edge” and I can’t wait to drive it. As for the X1, I doubt we will ever see it in the US because of the weak dollar. If BMW moved some production to Spartanberg it could make sense, but since the X1 is built in Austria it would probably be a looser for the company.

    • Anonymous

      The X1 is not built in Austria. It is built in Leipzig Germany. It is based on the E91 3er wagon.

      The MINI Countryman has replaced the X3 as being built in Austria by Magna.

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  • Anonymous

    The Honda S2000 made 120hp/L without turbos, although the torque was much less.

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