[jediali]

tricky one for me, in no particular order:

2.0TFSI - not very glamerous but the bread and butter of contemporary mainstream engine technology, such technology making it into other VAG engines (hence i wont add say the RS4 engine), no doubt VAG have best 4 cylinder german petrols IMO. Yes others sound better, are cheaper etc but this for me is more about leading particular markets.

BMW R6 straight 6

another benchmark ->

BMW's M54 inline-6 engine won praises all over the world. But the new R6 engine is better in every way, no matter power, weight or fuel consumption. In 2.5 and 3.0-litre form, it produces 218hp and 258hp respectively, compare with the old engine's 192hp and 231hp. This translate to 86-87hp per litre, the highest specific output of the class – we talk about mass production naturally aspirated engines of course.

The outstanding efficiency is contributed by several technologies. Like the outgoing engine, it has double Vanos continuously variable valve timing at all camshafts. What's new to the inline-6 is Valvetronic system, which eliminates throttle butterflies by varying valve lift according to throttle pedal. This reduces pumping loss at partial throttle, thus allows the R6 to drink 12% less fuel than the old engine.

In the past, the first generation Valvetronic used in BMW's V8 and inline-4 engines were seen as a fuel-reducing means rather than a power-enhancing design, although it is actually a variable valve lift system (think of Honda's VTEC). This was because the Valvetronic mechanism was heavy, limiting the revability of the engine. In the new R6 engine, the second generation Valvetronic employs aluminum parts to reduce moving mass. The camshafts are also converted to hollow type to save some 1.2 kg. This allow its variable lift function to excel at high rev, pushing maximum rev from 6500 rpm to 7000 rpm. This account for most of the power gain.

The R6 produces no more maximum torque than M54, but the torque curve is improved by using a 3-stage resonance variable intake system instead of the outgoing 2-stage system. For example, the 3.0 engine used to produce its maximum torque at 3500-4750 rpm. The new engine becomes 2500-4000 rpm.

Another advance is the use of electric water pump instead of engine-driven pump. It can save up to 2kW or 2.7 horsepower.

However, the biggest advance over M54 is weight reduction. Weighing 161kg only, it is claimed to be the world's lightest 6-cylinder engine, although Audi's 3.2 V6 is not far away at 169.5 kg. Contributing to the weight saving is the use of magnesium cam cover and the world's first magnesium-aluminum hybrid crankcase. The crankcase consists of 2 parts: magnesium housing and aluminum insert. The magnesium housing contains the oil channels and provides mountings for peripherals such as gearbox and alternator. The aluminum insert is employed to handle the high temperature and mechanical stress that magnesium cannot cope with. Despite of the addition of Valvetronic, the R6 is 10 kg lighter than M54.

The only weakness of R6 is the lack of space for enlargement. The 3.0 engine has a 85mm bore and 88mm stroke, while distance between bore center is just 91mm. That nearly rule out the possibility for enlargement. Most of its competitors now employ V6 engines displacing between 3.2 and 3.5 litres. Can the R6 find ways to increase power and, more crucially, torque in the future? or switch to turbocharging? I will be very interested to see.

This was obviously written before the direct injection version or TT DI version so I cant help but be impressed. This NA version was updated as you know to 272hp (called N52 now) and then they made N54:

The N54 engine employs a pair of small turbochargers to boost a very light pressure - only 0.4 bar. Therefore it produces "only" 34 more horsepower than the updated normally aspirated version, or a total of 306 horsepower at 5800 rpm. However, the small turbos in addition to the most sophisticated piezo direct gasoline injection (faster response than regular solenoid injectors) allows a normally aspirated-like compression ratio of 10.2:1 and a very strong torque curve, with a peak of 295 lbft (up 63 lbft) running continuously from 1300 rpm all the way to 5000 rpm. This made the variable intake manifolds and Valvetronic redundant, therefore discarded. The higher mechanical and thermal stress called for a negative change though: the magnesium outer crankcase is replaced by a conventional aluminum block with cast iron liners. At 190 kilograms the twin-turbo N54 is 28 kg heavier than the magnesium normally aspirated engine. Audi S4's 344hp 4.2-liter V8 is only 5 kilos heavier. Nevertheless, sticking with 6 cylinders allow the BMW engine to return remarkable frugality - 29.7 mpg according to EU combine cycle. Audi manages only 21.2 mpg.

Last but not least, and for a different perspective.

The engine as fitted to the Honda S600 /(also good in S800 form) for various interesting reasons. Jay Leno has a nice video on his garage web site detailing a restoration and technical overview.