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      04-30-2013, 10:30 AM   #23
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Probably not. We aren't likely to get such engine details until BMW is ready to release them, which will probably happen sometime later this year.



It is possible, sure, but not likely. Generally, higher RPM means less efficiency (its not necessily that simple of course, but typically that's how it works), and they are trying to maximize efficiency with their turbocharged engines.



The shape of the cylinder is not really important for max RPM. Rather, it is stroke length. The N55 and N63 have nearly identical stroke: 89.6mm and 89mm respectively. The 8000 RPM S54 has a similar stroke and Audi's V8 and V10 are actually 93mm and rev as high as 8500 RPM in some applications. Of course, those are all NA engines. The turbocharged McLaren engine has a very short stroke by comparison.



That would mean a brand new engine architecture with high costs. The whole point of working with an existing engine as a basis is to use existing tooling and maintain compatibility with some existing parts such as timing assembly, accessories, mounts, etc.

That is correct. What really makes the limits is the distance the piston has to travel, or piston movement in m/s. Long stroke plus high rev. equals high m/s and will turn in to higher friction and production of heat between the moving parts. There is no absolute high limit in piston velocity, this will depend of the
materials being used etc, but off course this is a cost matter.
N/A engines often have longer stroke vs bore to produce enough torque.
Since they are not TC they work with less pressure in the comb. chamber and
then again less force are put to the piston. And as we all know, force x arm=torque. Greater stroke also means greater arm made by the crankshaft.
TC-engines then have no problems producing high enough cyl. mean pressure/force to develop high torques, and do not have to compensate with longer stroke.
There is no thermal or force-related reasons why a TC engine cannot rev high
like a NA engine, its more the TCs ability to deliver enough boost at the end of the rev scale and the engine will often feel very dead at that point, loosing both power and torque. But I`m sure BMW are able to fix this problem with an important car like the M3/4.
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      04-30-2013, 02:05 PM   #24
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But I`m sure BMW are able to fix this problem with an important car like the M3/4.
Did BMW fix this problem with the M5? Or the M5 is not an important car?
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      04-30-2013, 03:29 PM   #25
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Did BMW fix this problem with the M5? Or the M5 is not an important car?
First of all, I`m not here to defend BMW in everything they do.

But I think BMW had a different focus with this gen. M5 compared to prev gen.
Through history M5 has been more of a soft famely car with high performance, think last gen were kind of a leap to the side as a more driver-focused car, like it or not. F10 has like stepped back into its natural habitat.

With the M3 its a different story, it has always built its reputation on handling and high-reving engines with proper throttle responce. Actually, in Europe the E92 got some criticism for being to soft and distanced from the driver. Anyway, I think BMW simply cannot afford to fail with the M3/4, it would destroy their reputation built up throughout the history of M3s. I have always thought that the day BMW put a TC-engine in the M3 would be the day we get a high reving TC engine without lag and with proper throttle responce in an affordable car, (excluding hypercars).
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      04-30-2013, 04:15 PM   #26
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With the M3 its a different story, it has always built its reputation on handling and high-reving engines with proper throttle response. Actually, in Europe the E92 got some criticism for being to soft and distanced from the driver. Anyway, I think BMW simply cannot afford to fail with the M3/4, it would destroy their reputation built up throughout the history of M3s. I have always thought that the day BMW put a TC-engine in the M3 would be the day we get a high reving TC engine without lag and with proper throttle response in an affordable car, (excluding hypercars).
I hope
I hope
I hope
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      05-01-2013, 11:55 AM   #27
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That is correct. What really makes the limits is the distance the piston has to travel, or piston movement in m/s. Long stroke plus high rev. equals high m/s and will turn in to higher friction and production of heat between the moving parts. There is no absolute high limit in piston velocity, this will depend of the
materials being used etc, but off course this is a cost matter.
N/A engines often have longer stroke vs bore to produce enough torque.
Since they are not TC they work with less pressure in the comb. chamber and
then again less force are put to the piston. And as we all know, force x arm=torque. Greater stroke also means greater arm made by the crankshaft.
TC-engines then have no problems producing high enough cyl. mean pressure/force to develop high torques, and do not have to compensate with longer stroke.
There is no thermal or force-related reasons why a TC engine cannot rev high
like a NA engine, its more the TCs ability to deliver enough boost at the end of the rev scale and the engine will often feel very dead at that point, loosing both power and torque. But I`m sure BMW are able to fix this problem with an important car like the M3/4.
Also, take note that the connecting rod length has as significant an effect upon max RPM, as does the piston mass and the total stroke length. It's not so simple as being over or under square.
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      05-02-2013, 07:10 AM   #28
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http://www.sportauto.de/marken/news/...g-7017765.html

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      05-02-2013, 07:35 AM   #29
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LOL
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      05-02-2013, 08:08 AM   #30
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Possibly a misprint. But perhaps someone just didn't get the memo.

When we look back on all of this V6 hubbub, the thing that strikes me most is how firmly that rumor stuck. Even today, we see people who should know better (enthusiast magazine writers and editors) still getting it wrong. Remember, the rumor originated as a direct quote from a BMW official. I think that this guy (I don't recall his name) was really pretty clever by floating this red herring out there. I know, I know - there are plenty of people who say BMW really was testing a V6 for possible production. Maybe, but I disbelieve. Of course, if spy pics ever come out to prove it I will happily eat my words. In the meantime, I give that guy props for his very effective smoke screen.
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      05-02-2013, 09:14 AM   #31
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Possibly a misprint. But perhaps someone just didn't get the memo.
But IF ... then the same misprint two times !!! And this magazin is "the german source" in case of sportcars, and why they should say V6, when all quotes I6, if they have no infos about this!?

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Originally Posted by mkoesel View Post
When we look back on all of this V6 hubbub, the thing that strikes me most is how firmly that rumor stuck. Even today, we see people who should know better (enthusiast magazine writers and editors) still getting it wrong. Remember, the rumor originated as a direct quote from a BMW official. I think that this guy (I don't recall his name) was really pretty clever by floating this red herring out there. I know, I know - there are plenty of people who say BMW really was testing a V6 for possible production. Maybe, but I disbelieve. Of course, if spy pics ever come out to prove it I will happily eat my words. In the meantime, I give that guy props for his very effective smoke screen.
Okay I also think it would be an I6, but some technical details make more sence if it would be an V6.
And if the engine description is really S55B30TO ... what do that meen?
I think it meens only next M-branch 6-cylinder engine after S54 this could be an I6 but also theoretical an V6.

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      05-02-2013, 03:16 PM   #32
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Also, take note that the connecting rod length has as significant an effect upon max RPM, as does the piston mass and the total stroke length. It's not so simple as being over or under square.
Off course, Einsteins theories regarding mass, velocity and force, or more known as E=mc2 will always be relevant when talking about engieering and physics.
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      05-03-2013, 07:07 AM   #33
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N/A engines often have longer stroke vs bore to produce enough torque.
Since they are not TC they work with less pressure in the comb. chamber and
then again less force are put to the piston. And as we all know, force x arm=torque. Greater stroke also means greater arm made by the crankshaft.
TC-engines then have no problems producing high enough cyl. mean pressure/force to develop high torques, and do not have to compensate with longer stroke.
For a given displacement, a longer stroke does not mean more torque. While it is true that a longer arm means more torque for a given force, this is offset by a smaller piston area on which the cylinder pressure is applied therefore yielding less force.
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      05-03-2013, 09:37 AM   #34
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For a given displacement, a longer stroke does not mean more torque. While it is true that a longer arm means more torque for a given force, this is offset by a smaller piston area on which the cylinder pressure is applied therefore yielding less force.
I had crafted a fairly involved response to this, but realized that it was more complex than I thought at first.

But, in short, cylinder count plays a role because, while it does not change total piston area, it does effect area per combustion event. So, assuming we have two engines with the same displacement, same stroke, same effective RPM range, but different cylinder count, the one with fewer cylinders theoretically has the torque advantage. This could partly explain why Porsche's H6 (in its most evolved form) has higher peak torque than BMW's S65 V8 at similar RPM.

But yes, generally speaking torque is displacement-bound (while power is RPM-bound). Most naturally aspirated production cars make somewhere in neighborhood of 75-85 ft-lbs of torque per liter at peak, whether they are econoboxes with tiny three or four cylinder engines or supercars with huge V12s.
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      05-03-2013, 09:56 AM   #35
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Off course, Einsteins theories regarding mass, velocity and force, or more known as E=mc2 will always be relevant when talking about engieering and physics.
Newton's theories.

But yeah, I just wanted to bring it up because, no one had mentioned it yet.
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      05-03-2013, 02:49 PM   #36
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I had crafted a fairly involved response to this, but realized that it was more complex than I thought at first.

But, in short, cylinder count plays a role because, while it does not change total piston area, it does effect area per combustion event. So, assuming we have two engines with the same displacement, same stroke, same effective RPM range, but different cylinder count, the one with fewer cylinders theoretically has the torque advantage. This could partly explain why Porsche's H6 (in its most evolved form) has higher peak torque than BMW's S65 V8 at similar RPM.

But yes, generally speaking torque is displacement-bound (while power is RPM-bound). Most naturally aspirated production cars make somewhere in neighborhood of 75-85 ft-lbs of torque per liter at peak, whether they are econoboxes with tiny three or four cylinder engines or supercars with huge V12s.
I am not sure I follow you here. For a total cycle (2 complete rotations), the area exposed to cylinder pressure should be the same regardless of cylinder count.

However, an engine with a larger cylinder count will have more friction losses. Just considering the piston/cylinder interface, the bigger pistons have a better area to circumference ratio.
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      05-03-2013, 03:19 PM   #37
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I am not sure I follow you here. For a total cycle (2 complete rotations), the area exposed to cylinder pressure should be the same regardless of cylinder count.
That's true, but - and this gets into the complexity that I was talking about earlier - the summation of all the forces on the crankshaft at any particular instant will be limited by the maximum force applied during a single combustion event.

Even if we assume zero friction in the system (just for simplicity), the more cylinders the engine has, the smaller the maximum force available to act on the crankshaft. Consider a 100 or 1000 or 1000000 cylinder engine. One tiny piston applying force to the rotating mass at any given time. As cylinder count goes up toward infinity, there is not even enough force to turn the engine over. As it goes down toward 1, that force is maximized. It is true that more cylinders mean more chances for combustion. However, it is a bit like beating on a piece of sheet metal with a sledge hammer once every few seconds vs. tapping on it with your fingers very quickly. The former has a much more significant effect. Okay, well your fingers don't have as much mass as a sledge hammer - so lets use a rubber mallet instead, and maybe you are wearing some serious SuperBowl-ring-like bling on each of your fingers when you are doing the tapping. Still, you get further with the mallet.

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However, an engine with a larger cylinder count will have more friction losses. Just considering the piston/cylinder interface, the bigger pistons have a better area to circumference ratio.
Yes, and that's a good point. However this is true only assuming a similar compression ratio since a higher compression engine will require a larger ring- to-cylinder contact area to avoid excessive blow-by.
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      05-03-2013, 04:09 PM   #38
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For a given displacement, a longer stroke does not mean more torque. While it is true that a longer arm means more torque for a given force, this is offset by a smaller piston area on which the cylinder pressure is applied therefore yielding less force.
OK, my explanation above was very simple and imcomplete, just to show typical different between NA and TC engines.
In theory you are right, given displacement and the differences will weigh up for each other, but in real life that will not be the case. I was a bit categorical when I stated that longer stroke equals higher torque.
Will try to explain a bit more:
Given two NA engines with different stroke but same volume, rpm etc. Also we say they have the same exh/inl-valves, timing, inlet and exh systems, (this will not be natural since they will breathe differently, but just now that will be the case just to simplyfie things).
The one with a slight longer stroke will achive better "filling grade" given the same conditions, (by filling grade I mean the engines ability to fill the cyl with fresh air, M engines vary between 100 to 110% filling, this means theoretically a cyl with displacement of 1 litre will fill up with 1,1litre air during inlet-stroke=110%)
The reason for this is that is that the "long-stroke engine" have better ability/longer period of time to create "speed" on the inlet air through the ducts, (due to the slight longer stroke) and thus continue to fill with air after BDC in the inlet stroke and again create a slight above atm pressure in the cyl. This again will create better combustion->higher pressure->increased force->higher torque.
Please bare in mind that this is just one of and a quite cost effective ways to create better breathing or filling grade of a NA engine, there are many ways to the goal as usual, many of them much more expensive. F1 engines for example are not very long stroked, but still create a filling grade up to 130% or more, (but those engines are far from cheap
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      05-03-2013, 10:05 PM   #39
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That's true, but - and this gets into the complexity that I was talking about earlier - the summation of all the forces on the crankshaft at any particular instant will be limited by the maximum force applied during a single combustion event.

Even if we assume zero friction in the system (just for simplicity), the more cylinders the engine has, the smaller the maximum force available to act on the crankshaft. Consider a 100 or 1000 or 1000000 cylinder engine. One tiny piston applying force to the rotating mass at any given time. As cylinder count goes up toward infinity, there is not even enough force to turn the engine over. As it goes down toward 1, that force is maximized. It is true that more cylinders mean more chances for combustion. However, it is a bit like beating on a piece of sheet metal with a sledge hammer once every few seconds vs. tapping on it with your fingers very quickly. The former has a much more significant effect. Okay, well your fingers don't have as much mass as a sledge hammer - so lets use a rubber mallet instead, and maybe you are wearing some serious SuperBowl-ring-like bling on each of your fingers when you are doing the tapping. Still, you get further with the mallet.
I'm still not following, maybe it's just me that is thick .

Let's assume the 1000000 cylinder engine example you mention. Maybe one cylinder will not be able to turn the crank. However with that many cylinders, way more than one cylinder is pushing on the crank at any given time (250000 of them actually). The combined forces of all these cylinders should yield the same average torque than a lower cylinder count engine.

Further, to evaluate torque, I don't think it is representative to measure instantaneous torque. An average output will give better representation of an engine capabilities. If you take the other extreme of an example, a one cylinder engine. Such an engine produces torque for only about half a revolution of every two rotations. It also needs to rely on a heavy flywheel to store energy for its compression cycle. So yes, it is quite torquey on the power stroke, but the rest of the time...

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Yes, and that's a good point. However this is true only assuming a similar compression ratio since a higher compression engine will require a larger ring- to-cylinder contact area to avoid excessive blow-by.
Agreed. I assumed everything being equal except cylinder count.

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      05-03-2013, 10:18 PM   #40
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OK, my explanation above was very simple and imcomplete, just to show typical different between NA and TC engines.
In theory you are right, given displacement and the differences will weigh up for each other, but in real life that will not be the case. I was a bit categorical when I stated that longer stroke equals higher torque.
Will try to explain a bit more:
Given two NA engines with different stroke but same volume, rpm etc. Also we say they have the same exh/inl-valves, timing, inlet and exh systems, (this will not be natural since they will breathe differently, but just now that will be the case just to simplyfie things).
The one with a slight longer stroke will achive better "filling grade" given the same conditions, (by filling grade I mean the engines ability to fill the cyl with fresh air, M engines vary between 100 to 110% filling, this means theoretically a cyl with displacement of 1 litre will fill up with 1,1litre air during inlet-stroke=110%)
The reason for this is that is that the "long-stroke engine" have better ability/longer period of time to create "speed" on the inlet air through the ducts, (due to the slight longer stroke) and thus continue to fill with air after BDC in the inlet stroke and again create a slight above atm pressure in the cyl. This again will create better combustion->higher pressure->increased force->higher torque.
Please bare in mind that this is just one of and a quite cost effective ways to create better breathing or filling grade of a NA engine, there are many ways to the goal as usual, many of them much more expensive. F1 engines for example are not very long stroked, but still create a filling grade up to 130% or more, (but those engines are far from cheap
I am not sure I am reading you right. My understanding is that for a given RPM and displacement, the quantity of air to fill a cylinder and the time it takes to do so are exactly the same regardless of bore and stroke. So the charge velocity in the intake tract would be exactly the same (if we assume same valve size as you stated).

However, the engine with the larger bore can have an advantage at higher RPM because bigger valves can be fitted, thus increasing volumetric efficiency.

I also highly doubt that the S65 has a volumetric efficiency higher than 100%. There was a good discussion in another thread on this topic. My guess is that a volumetric efficiency between 80% and 85% at power peak is more realistic.

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      05-04-2013, 02:40 AM   #41
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I am not sure I am reading you right. My understanding is that for a given RPM and displacement, the quantity of air to fill a cylinder and the time it takes to do so are exactly the same regardless of bore and stroke. So the charge velocity in the intake tract would be exactly the same (if we assume same valve size as you stated).

However, the engine with the larger bore can have an advantage at higher RPM because bigger valves can be fitted, thus increasing volumetric efficiency.

I also highly doubt that the S65 has a volumetric efficiency higher than 100%. There was a good discussion in another thread on this topic. My guess is that a volumetric efficiency between 80% and 85% at power peak is more realistic.
You have to excuse my language skills, Volumetric efficiency was what I ment when I said "filling grade". Best VE are measured at torque peak, not power peak. S54B32 has a best VE of 106% in the standard E46 M3, and even higher in the CSL,(dont know the excact number here). Normaly VE will be a bit lower in V8s but as low as 80-85%?
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      05-04-2013, 06:25 AM   #42
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However with that many cylinders, way more than one cylinder is pushing on the crank at any given time (250000 of them actually).
In all modern automobile combustion engines only one cylinder fires at a time. So I was assuming the same for my hypothetical engine examples.

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Further, to evaluate torque, I don't think it is representative to measure instantaneous torque.
Agree. But like I said, peak torque is still ultimately bounded by torque at any given instant, which in turn is a function of the force at that instant.

It's just like my last example. Sure you can get a lot more finger taps in than hammer swings over a given period of time. But you still never make any significant dents in the sheet metal.
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      05-04-2013, 06:38 AM   #43
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Originally Posted by Inge_F View Post
You have to excuse my language skills, Volumetric efficiency was what I ment when I said "filling grade". Best VE are measured at torque peak, not power peak. S54B32 has a best VE of 106% in the standard E46 M3, and even higher in the CSL,(dont know the excact number here). Normaly VE will be a bit lower in V8s but as low as 80-85%?
You are correct, peak volumetric efficiency is reached at torque peak. I should have quoted 90-95% VE at torque peak instead of the 80-85% at power peak. It was a bit late at night when I posted...

Can you quote the source of the 106% VE for the S54B32? I am very surprised by this high number. Street cars with their intake and exhaust plumming, filters and catalytic converters have quite a lot of restrictions that hamper VE. There was another thread on the topic of VE, there were a lot of assumptions but not many hard facts.

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      05-04-2013, 06:53 AM   #44
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In all modern automobile combustion engines only one cylinder fires at a time. So I was assuming the same for my hypothetical engine examples.
It is true that only one cylinder spark plug "fires" at once. However the power stroke, the time positive cylinder pressure applies force on the piston, lasts about half a revolution. So for engines with more than four cylinders, power strokes will overlap.

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Originally Posted by mkoesel View Post
Agree. But like I said, peak torque is still ultimately bounded by torque at any given instant, which in turn is a function of the force at that instant.

It's just like my last example. Sure you can get a lot more finger taps in than hammer swings over a given period of time. But you still never make any significant dents in the sheet metal.
The sledgehammer example is not really representative because it refers to an impact. If you have 100 fingers pushing on a object with 1lb each, it will yield the same force as a person leaning with his shoulder on the object with 100lbs.

Since peak torque is measured for a given RPM, I still think torque of the engine pulses need to be averaged to properly reflect an engines abilities.

Last edited by CanAutM3; 05-04-2013 at 07:03 AM.
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