The M54 is the old 3,0 injection engine. The new N54 is repleacing it.
The most obvious difference is, that the new N54 engine has a direct fuel injection. The N54 is a so cold SI engine = Straight Injection.

Oh a little small thing i have forgot. The N54B30 is the new 3,5 litres gasoline engine which has the bi-turbo system in it. 

I thought the R6 engine had a magnesium crankcase and the N54 an aluminum crankcase with cast-iron liners 

From reading the description of the N54 turbo it doesn't look like it makes use of BMW's patented valvtronic design like all the other new engines. Despite this, the new turbo has a great torque cruve with 290+ torque from 1500 RPM to near red line. The valvtronic in the N52 for example added 1/3 extra weight, but since it also made use lighter magnesium in its crankshaft the overall weight was 20 kg or so less that the privious E46 3.0 liter I-6. This new engine is pure aluminum and doesn't make use of weight saving magnesium, but if it really doesn't have valvtronic than this is off-set. I will be very interested to see what the weight of the 335 sedan vs the 330 sedan will be and how close to a 50 -50 front-rear weight distribution it will have. The dual exhaust in the rear will probably balance off the added weight in the front to help the 50-50 weight distribution goal. I wonder if excluding the valvtronic saves them nearly the same amount in production costs that adding the bi-turbo adds to the costs and hence they will be able to sell them for almost the same price.


From BMW Press Club Site (German):

N54 Bi-Turbo engine with HPI direct injection.
306HP, 400Nm available in range 1500 to 5800rpm. Max 7000 rpm. With full alluminium crankshaft casing, Bi-VANOS, electric water pump. 70kg less weight than 4.0L V8 NA engine. No turbo lag.

Tested in E90:
80-120kmh in 6.3s (eg. 330i in 8.2s)
0-100kmh in 5.7s (eg. 330i in 6.3s)


Google translation of press release:


can be found here
http://www.auto-motor-und-sport.de/news/auto_und_produkte/bmw_neuer_top_sechszylinder.104140.htm


The result is readable in the values of 225 kW/306 HP as well as the maximum torque of 400 Newtonmeters and witnesses from an impressing and already thrust using at low numbers of revolutions. Which means this for the driving experience, the engine developers by the example of a sedan of the BMWS of 3series row calculated: In acceleration from zero on 100 km/h the Bi-turbo--variant would be therefore faster around more than a half second, the elasticity value (80 to 120 km/h in the second highest course) could itself from 8.2 seconds for the strongest suction engine variant, which BMW 330i, on 6.3 seconds to improve. While maintaining the suction engine concept a such increase in dynamics would have been realizable only by a substantial extension of the capacity, connected with an appropriate gewichtszunahme and the effects resulting from it on the vehicle balance. On the other hand proves the employment of the turbocharger technology in connection with the High Precision Injection as a particularly efficient method, in order to fulfill still higher requirements to the achievement and the torque of the engine. To the comparison: The new Reihensechszylinder Bi turbo weighs about 70 kilograms less than a similarly high performance eight-cylinder August engine with a capacity of 4,0 litres. Beyond that exhibits the engine equipped with High Precision Injection opposite a equivalent strong turbo engine with suction tube injection a consumption advantage of approximately ten per cent.

Apart from the small weight and the values consumed favorable for its performance class the new Bi-turbo--drive can offer a further quality criterion of the row six cylinder engines of BMW. It offers outstanding quiet running and thus exactly that virtue, with which the row six cylinder engines became propulsion technology, cultivated recognized world-wide, from BMW to the yardstick for. Already the cylinder arrangement gives a balanced character to the engine concerning the free mass forces - also at high numbers of revolutions the engine acts vibration-free. In addition had also the turbo-variant of the six-cylinder of the suction engine particularly light cam shafts, the variable cam shaft adjustment double VANOS admitted as well as over an electrically operated water pump, which works only according to the respective cooling need.

The turbo-hole is past. With the new engine variant engineers of BMW succeeded in eliminating the construction dependent disadvantages of earlier turbo-prop engines. Therefore the loaded six cylinder of BMW does not show also for turbo engines to today typical characteristics: The thrust only using with delay is just as strange to the new drive as the high fuel consumption of conventional turbo aggregates. For a clearly more spontaneous achievement development provides in particular the Bi-turbo--concept. In place of a large loader two smaller copies supply in each case three cylinders with compressed air. Substantial advantage of the small dimensioned loaders is their small moment of inertia. Already the easiestImpulse, which the driver with the accelerotor pedal produces, is answered with immediate pressure build-up. The turbo-hole - that moment, which passes, until the loader takes up its work-promoting effect -, so far typical with loaded engines, is not perceptible therefore any longer. In driving the rating of the new turbo-prop engine resembles therefore the force development of a clearly capacity-stronger suction engine. 3.0 available the litre aggregate makes its imposantes torque of 400 Newtonmeters without noticeable delay and over the broad number of revolutions breakdown from 1500 to 5,800 min-1 away. And thus not enough: The engine winds up strong into the range from 7,000 min-1. The driver particularly experiences one sovereigns form of the dynamics, which it him permitted to complete also brisk acceleration maneuvers eases.

Double progress: high achievement, high efficiency. In order to bring a fascinating driving experience with values consumed up-to-date in agreement, BMW developed a row six cylinder petrol engine with Bi-turbocharger, fuel direct injection and full aluminum crank case as world-wide first a car manufacturer. The conception of the turbochargers already makes a contribution for consumption reduction. Because the turbines consist of high-temperature resistant special steel and bear temperatures of up to 1050 degrees, can be done without the refreshing effect of a increased fuel supply. Straight ones under full load result from it noticeable consumption reductions.

The key function in the concept for as economical a handling fuel as possible comes however the High Precision Injection. The new generation of gasoline direct injection fulfills also in practice expectations set into it regarding economy, without thereby reductions would be necessary with the dynamic qualities of the engine. High Precision Injection permits a more accurate mixture dosage as well as a higher compression - ideal conditions for an increase of the efficiency and a clear reduction of consumption. This becomes possible due to the central placement of the Piezo injector between the valves. In this position the new injector opening outward can distribute the fuel conically and particularly evenly in the combustion chamber. With the development of the new row six-cylinder with Bi-turbocharger and direkteinspritzung BMW opens a new chapter for already an engine principle quite old in the reason. Nevertheless could only recently the 100. "birthday" of the turbo engine to be celebrated. In November 1905 of Swiss engineer Alfred Buechi to the patent announced loader


from what it seems its so far it has a full aluminium crankcase, as soon as i find anything else you guys(gals) will be the first to know

And ofcourse more info on BMW Heaven :
http://bmwheaven.bmwsport.net/content/view/75/3/

Thanks a heap for the info.
The link below concerns an online knowledge-site, if one for instance types BMW N62 in the search-space, one gets all the N62 related V8 engines.
Such as N62B40 ( 4 liter V8 , not yet the new M3 V8 of 425 HP, but its the same engine-block)

http://en.wikipedia.org/wiki/List_of_BMW_engines

In 2007 BMW introduces the bi-turbo 3 liter straigt six as the N54 engine ( which is not completely new ).
My guess is that this is for a reason, otherwise BMW would have chosen for the magnesium R6 version, which powers the 330i, the 130i and so on.
The weight of this magnesium engine is 161 kg and 70 kg leigther than the new 4 liter 425 hp M3 V8 ( thus weighing a hefty 230 kg ).
My guess is that N54 3 liter straigt six is somewhat heavier than the R6 variant, lets say about 20 kg.
Would the N54 be 70 kg lighter than the 4 liter V8 than this V8 becomes allmost as heavy as the OM629 4 liter V8 turbo-diesel ( 259 kg ).

Wikipedia is a great source for a lot of stuff, but also my site has a list of engines and the cars that are related to it: http://bmwheaven.bmwsport.net/component/option,com_bkbsearch/Itemid,9/func,bkbengines/ (not as much info as wikipedia, but enough for now).

And I think that the M3 engine will also be released in the "M4" (still don't know what's going to be called a 4series and what a 3series...?)

sweet!