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      09-25-2013, 03:51 PM   #1
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Update: False. S55 engine has oversquare bore/stroke and shares "nothing" with N55!

The M3/M4 tech specs has been revised to include the following:


•3.0L inline 6 cylinder engine (S55) with two mono-scroll turbochargers
◦3,027 cc (compare to 2,979 cc of N55)
89.6mm over-square bore / 80mm stroke (compare to 89.6mm stroke / 84mm bore of N55)
◦Derived from N55 engine
◦Direct Injection
◦closed-decked crankcase (4.4 lbs / 2kg lighter)
twin-wire arc-spray coating (instead of liners) in cylinder bores reduce engine weight
◦20 lbs lighter than V8 S65 engine (from E90/E92 M3)
•430 HP (approximately) from around 5000-7300 RPM
•"far beyond" 369+ LB-FT (500 Nm) from under 2000 RPM to over 5000 RPM
•See Dyno Chart
•Slightly above 7500 RPM redline
That is interesting and points to some real engine development work being undertaken by BMW M (if info is correct).

The short stroke is good for high rpm and lowering piston speeds at high rpm. It will also give it a more rev willing character and sharper response.

I suspect that the tech used instead of cylinder liners is what allows for the big bore in the N55 engine.

The bore/stroke really sets this engine apart from the 335i (N55) engine and is nothing that a tuned 335i can compensate for. The engine's will act, feel and sound different.

According to Auto Motor und Sport the block is a brand new development with focus on strength and light weight:

Der Block ist eine komplett neue Entwicklung mit Fokus auf Standfestigkeit und Leichtbau.
Further they claim the following hp and torque ranges:

-Maximum HP between 5500-7200rpm (should be 5700-7200rpm)
-Maximum torque between 1800-5700rpm

EDIT 26.09.2013:

Here is what UK magazine CAR writes after the workshop:

Rumours of a V6 triple-turbo circulated early in the M3/M4's development but the production unit is a 3.0-litre straight six with two turbochargers, and an over-square bore of 89.6mm and 80mm stroke. It shares nothing other than peripheral ancillaries with BMW's other straight-six petrol engine, but the familiar design has allowed BMW to retain the production infrastructure to build it, saving money to reinvest back into other weight-saving measures without drastically increasing the price of a relatively cost-sensitive performance car. This means that the M3/M4 range should still retail from around £60k when it goes on sale next year.
Interesting info about the engines ability to add boost to maintain power at high altitudes and temperatures:

The turbos run at a maximum of 1.25 bar boost but often less, the electronic brain only cranking up to that level of pressure under high operating temperatures or at high altitude. It means the power and torque figures will remain consistent in the vast majority of conditions. As Vice President of engineering, Albert Biermann, explains, that means a standard M3/M4 will often be as fast on track as a tuned car with a claimed additional 50bhp but no extra leeway to continue to develop that power as operating temperatures soar.
while BMW promises that the small, fast-acting turbos (smaller than those in the 1M, in fact), together with flow-enhanced manifolds and an intercooler that sits adjacent to the inlet tract help to deliver the instantaneous responses that M fans know and love

CanAutM3 has pointed out that there seems to be a slight "problem" with the quoted HP and Torque figures:

As an observation, those numbers cannot be correct.

-Maximum HP between 5500-7200rpm (should be 5700-7200rpm)
-Maximum torque between 1800-5700rpm

The torque and power plateau cannot overlap (5500-5700RPM). Using the assumption of 430hp and 395lb-ft, the transition from the torque plateau to the power plateau should be around 5700RPM.
BMW's dyno chart actually shows that there isn't a overlap of HP and Torque... So, spot on observation

And, finally a picture of the block:

To me, this makes the S55 a genuine M engine

A few pictures of the N55 for comparison:
Attached Images

Last edited by Boss330; 09-27-2013 at 03:12 AM..