Update: False. S55 engine has oversquare bore/stroke and shares "nothing" with N55!

[Boss330]

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
◦VALVETRONIC
◦Double-VANOS
◦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

http://www.auto-motor-und-sport.de/n...n-7741783.html


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

http://www.carmagazine.co.uk/News/Se...he-M3-V8-2013/

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:

[Jason]

Sorry for the confusion. Fixed to be clearer now.

3.0L inline 6 cylinder engine (S55) with two mono-scroll turbochargers

• 3,027 cc (compare to 2,979 cc of N55)
• 89.6mm bore / 80mm stroke over-square (compare to 84mm bore / 89.6mm stroke under-square of N55)

[Needsdecaf]

Thanks!

9mm reduction in stroke is huge! So much for those who said its a tubed N55

[Boss330]

Originally Posted by Jason

Sorry for the confusion. Fixed to be clearer now.

Thanks.

I noticed the reversed figures for the N55 and therefore initially added the words "bore" and "stroke" behind the N55 numbers in my post to avoid the confusion

[NISFAN]

Originally Posted by Needsdecaf

Thanks!

9mm reduction in stroke is huge! So much for those who said its a tubed N55

That would represent a huge drop in torque.

I'm liking the full counterbalance crank

[Needsdecaf]

Originally Posted by NISFAN

That would represent a huge drop in torque.

It would appear not to however, no ? That is certainly true when it comes to N/A emgines, but we are talking FI here.

It is significant because it should be much freerer revving than the lazy n55.

[Boss330]

Originally Posted by NISFAN

That would represent a huge drop in torque.

I'm liking the full counterbalance crank

In a NA engine more so than in a Turbo'd engine. You can compensate for less torque from the engine by adding boost so that it makes up the torque deficit when on boost.

But a comparable engine, but with longer stroke, would make more torque under same boost conditions. Or the same torque with less boost.

But I'd rather have a bit higher boost to compenaste the torque lost due to shorter stroke and the higher rpm/lower piston speeds possible on a short stroke engine.

It should feel much more alert than a "lazy" N55 335i.

[NISFAN]

Originally Posted by Needsdecaf

It would appear not to however, no ? That is certainly true when it comes to N/A emgines, but we are talking FI here.

It is significant because it should be much freerer revving than the lazy n55.

Originally Posted by Boss330

In a NA engine more so than in a Turbo'd engine. You can compensate for less torque from the engine by adding boost so that it makes up the torque deficit when on boost.

But a comparable engine, but with longer stroke, would make more torque under same boost conditions. Or the same torque with less boost.

But I'd rather have a bit higher boost to compenaste the torque lost due to shorter stroke and the higher rpm/lower piston speeds possible on a short stroke engine.

It should feel much more alert than a "lazy" N55 335i.

None the less, stroke length has the same effect in FI as NA. Obviously the torque is still good despite the reduced stroke, but as you say this is likely to come from higher boost.

A side effect of the short stroke, is the cylinder pressure will still be very high at end of stroke, which means more pressure to power the turbo.

[Needsdecaf]

Originally Posted by NISFAN

None the less, stroke length has the same effect in FI as NA. Obviously the torque is still good despite the reduced stroke, but as you say this is likely to come from higher boost.

A side effect of the short stroke, is the cylinder pressure will still be very high at end of stroke, which means more pressure to power the turbo.

Yes, another benefit.

[Holset]

Good news!

Bigger bore is better for top end power.

[stefan]

I really hoped they could find a way to stretch the position of peak hp, but I think what they've done here is struck a good balance between fuel economy and the ability to still track the car to an extent. It will not be able to compete on a track with an NA engine of similar peak power, but hey. It will be great for DD'ing. Welcome to 2013 I guess!!

Not using liners is a surprise to me. M must have done their homework.

[Yellow Snow]

89.6mm bore really does mean this block is completely redesigned.

Cylinder spacing of the small block 6 has always been 91mm.

It's not possible to run with a 1.4mm wall thickness, so it looks like tuning options with the wider bore spacing could reap better rewards than first thought.

[DylanBerg]

Comparison photo of S55 and an N55

[Needsdecaf]

Nice shots. Ironically, the heads look a lot more similar than the blocks.

[sparkyg]

I hope you guys are right.

We have nothing to go on other than DTM drivers.

[Boss330]

Originally Posted by sparkyg

I hope you guys are right.

We have nothing to go on other than DTM drivers.

Right about bore/stroke or engine characteristics?

Bore/stroke is apparently from BMW so I hope this turns out to be correct

Engine characteristics is just, from my standpoint, based on engineering principles related to long vs short stroke. A short stroke engine is by definition able to rev higher at lower piston speeds and has sharper response. There's less inertia to overcome when accelerating the crank on a short stroke engine.

How THIS engine feels we don't know yet, but by definition it should be more responsive than the N55 (unless BMW M has engineered it to feel lazy...)

[mkoesel]

What is the bore center dimension of the S55?

I am having a very hard time believing that they've increased the bore center only to achieve essentially no displacement increase. Sure, the stroke decrease is great, but they've avoided it for years with the S50->S52->S54 even as RPMs were pushed higher and piston speeds went up and up. Why the change now?

If we really do get a new longer block, then this is arguably the single biggest piece of engine news from BMW since they reintroduced turbocharging seven years ago. It would mean a square bore 89.6 x 89.6 3.4L engine is possible - the first time we can (safely, reliably) go over 3.2L with a BMW I6 since they retired the "Big Six" decades ago. And without resorting to an iron block as every OEM I6 engine above 3L from BMW has used.

And if we don't get a new bore spacing, I am at a complete loss for words as far as the incredible 1.4mm between cylinders.

[Boss330]

Originally Posted by mkoesel

What is the bore center dimension of the S55?

I am having a very hard time believing that they've increased the bore center only to achieve essentially no displacement increase. Sure, the stroke decrease is great, but they've avoided it for years with the S50->S52->S54 even as RPMs were pushed higher and piston speeds went up and up. Why the change now?

If we really do get a new longer block, then this is arguably the single biggest piece of engine news from BMW since they reintroduced turbocharging seven years ago. It would mean a square bore 89.6 x 89.6 3.4L engine is possible - the first time we can (safely, reliably) go over 3.2L with a BMW I6 since they retired the "Big Six" decades ago. And without resorting to an iron block as every OEM I6 engine above 3L from BMW has used.

And if we don't get a new bore spacing, I am at a complete loss for words as far as the incredible 1.4mm between cylinders.

Good points.

I hope that what we see is the basis of what happened with the E36 engine. First a 3l then a later version with 3,2l. This engine leaves (possibly) room for displacement upgrades down the road and/or CSL type versions with larger volume than the std. engine...

On a NA engine they wanted the longest stroke possible to gain some torque for driveability, hence why the old engines had a fairly long stroke. On the S55 the FI takes care of the torque deficit present in a short stroke engine. You can have your cake and eat it Both short stroke and high torque

[mkoesel]

Originally Posted by Boss330

Good points.

Thank you.

On a NA engine they wanted the longest stroke possible to gain some torque fro driveability, hence why the old engines had a fairly long stroke.

But, torque changes achieved solely by adjusting bore and stroke at a specific fixed displacement are of minimal significance in the overall picture. With so many other factors affecting the engine's output characteristics, attacking the bore dimensions simply to achieve a torque increase is not cost effective in general.

On the S55 the FI takes care of the torque deficite present in a short stroke engine. You can have your cake and eat it Both short stroke and high torque

I am not so convinced. I disbelieve that if we built a 3.2L naturally aspirated I6 engine using the 89.6mm of the S55 at 360hp (a power figure which BMW did reach in the CSL), that there would be any valid claims of a torque issue. Such claims would boil down to the same rhetoric we endure with respect to the S65 and S85. And speaking of that, what happened to this under-square, high revving alleged high torque design of the S54 once they got ahold of the 98mm bore spacing? Surely we cannot honestly believe the huge increase in bore and huge decrease in stroke was all done at the expense of a supposedly superior higher torque design of the past I6, all while the ability to reverse the bore dimensions to over-square just happened to conveniently and coincidentally present itself.

Color me a very deep shade of skeptical.

Getting back to the S55, I accept that the new spray on lining allows for a larger bore. But I still think the bore center must be greater than 91 mm now and I am very eager to know if this is the case.

Yep I'm thinking the lack of liners allowed them to increase the bore without lengthening the block.

I wonder if this is the same liner-less tech Ford came up with and is used on the GTR, according to this article on jalopnik, the benefits of this showed during Fords testing at 250k miles the hone pattern was still there, virtually no wear, the coating acts like a sponge pours creating a very good bearing surface.


http://jalopnik.com/5467038/the-ford...he-nissan-gt+r

[Diagnosic]

It will be very interesting to compare the new M3/M4 with the already available Alpina B3 Biturbo F30 (also with xDrive):
-410 HP
-600 NM
-0 - 100 in 4 seconds (with xDrive).

I will have a testdrive with the Alpina on October 4th

[Boss330]

Originally Posted by mkoesel

Thank you.



But, torque changes achieved solely by adjusting bore and stroke at a specific fixed displacement are of minimal significance in the overall picture. With so many other factors affecting the engine's output characteristics, attacking the bore dimensions simply to achieve a torque increase is not cost effective in general.



I am not so convinced. I disbelieve that if we built a 3.2L naturally aspirated I6 engine using the 89.6mm of the S55 at 360hp (a power figure which BMW did reach in the CSL), that there would be any valid claims of a torque issue. Such claims would boil down to the same rhetoric we endure with respect to the S65 and S85. And speaking of that, what happened to this over-square, high revving alleged high torque design of the S54 once they got ahold of the 98mm bore spacing? Surely we cannot honestly believe the huge increase in bore and huge decrease in stroke was all done at the expense of a supposedly superior higher torque design of the past I6, all while the ability to reverse the bore dimensions to under-square just happened to conveniently and coincidentally present itself.

Color me a very deep shade of skeptical.

Getting back to the S55, I accept that the new spray on lining allows for a larger bore. But I still think the bore center must be greater than 91 mm now and I am very eager to know if this is the case.

A oversquare design is better for a high revving engine as that keeps piston speeds down. Lower piston speeds is good for durability. One of the disadvantages of a oversquare (short stroke) is lack of/less torque than a similarly sized undersquare engine.

Remember that a long stroke means a longer arm from crankpin to crank center, and as we all know Torque = Force x Arm. So the longer the stroke, the longer the arm from crankpin to crank centre is and more torque is made.

However on a FI engine, boost can be increased to make up for the torque deficit. In a high performance FI engine then, a oversquare design makes a lot of sense because it has so many advantages over a undersquare design. So, no this didn't happen by coincidence. A large bore/short stroke gives many advantages in breathing (larger valves), less friction, less heat, lower piston speeds. In a high perf engine a large bore/short stroke will allmost allways be the best solution for high end power, high rpm and agility. With FI you can also compensate for less torque, which the old M3 engines couldn't.

The magnitude of torque depends on three quantities: the force applied, the length of the lever arm[2] connecting the axis to the point of force application, and the angle between the force vector and the lever arm.

An oversquare engine allows for more and larger valves in the head of the cylinder, lower friction losses (due to the reduced distance travelled during each engine rotation) and lower crank stress (due to the lower peak piston speed relative to engine speed). Due to the increased piston- and head surface area, the heat loss increases as the bore/stroke-ratio is increased excessively. Because these characteristics favor higher engine speeds, oversquare engines are often tuned to develop peak torque at a relatively high speed.

Undersquare engines

These produce strong torque at low to mid range rpm's because of the "leverage" advantage of a longer stroke. But, undersquare can be a negative trait, since a longer stroke usually means greater friction, a weaker crankshaft and a smaller bore means smaller valves which restricts gaseous exchange; however, modern technology has lessened these problems (explanation?). An undersquare engine usually has a lower redline, but should generate more low-end torque. In addition, a longer stroke engine can have a higher compression ratio with the same octane fuel compared to a similar displacement engine with a much shorter stroke ratio. This also equals better fuel economy and somewhat better emissions. Going undersquare can cause pistons to wear more quickly (greater side-loads on the cylinder walls) and can cause ring seal problems and lubrication problems; with increased loads on the crankshaft, pistons, the piston pins, connecting rods, and rod bearings (due to piston speed). In general, a longer stroke leads to higher thermal efficiency through faster burning and lower overall chamber heat loss. A longer stroke will have greater port velocity at a given RPM, more torque due to more leverage on the crank, will achieve it's greatest efficiency at a lower RPM. Smaller combustion chambers are also more efficient, with the flame front having a shorter distance to travel- this leads to being more detonation resistant, and having an advantage for emissions.


Oversquare engines

These are generally more reliable, wears less, and can be run at a higher speed. In oversquare engines power does not suffer, but low-end torque does - it being relative to crank throw (distance from the crank center to the crankpin). An oversquare engine cannot have as high a compression ratio as a similar engine with a much higher stroke ratio, and using the same octane fuel. This causes the oversquare engine to have poorer fuel economy, and somewhat poorer exhaust emissions. Breathing is an important advantage for oversquare engines, as the edges of the valves are less obstructed by the cylinder wall (called "unshrouded"). The big bore can fit larger (or more) valves into the head and give them more breathing room.

With shorter crankshaft stroke (and therefore piston travel) parasitic losses are reduced. Ring drag is the major source of internal frictionand the crankshaft assembly also rotates in a smaller arc, so the windage is reduced. Oil-pressure problems caused by windage and oil aeration are lessened.