04-30-2013, 10:30 AM | #23 | |
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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. |
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04-30-2013, 02:05 PM | #24 |
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04-30-2013, 03:29 PM | #25 | |
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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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05-01-2013, 11:55 AM | #27 | |
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05-02-2013, 07:10 AM | #28 |
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05-02-2013, 07:35 AM | #29 | |
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05-02-2013, 08:08 AM | #30 | |
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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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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. Greets Uli_HH |
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05-02-2013, 03:16 PM | #32 |
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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.
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05-03-2013, 07:07 AM | #33 | |
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05-03-2013, 09:37 AM | #34 | |
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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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05-03-2013, 02:49 PM | #36 | |
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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. |
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05-03-2013, 03:19 PM | #37 | ||
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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. Quote:
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05-03-2013, 04:09 PM | #38 | |
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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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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... Agreed. I assumed everything being equal except cylinder count. Last edited by CanAutM3; 05-03-2013 at 10:45 PM.. |
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05-03-2013, 10:18 PM | #40 | |
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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. Last edited by CanAutM3; 05-03-2013 at 10:52 PM.. |
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05-04-2013, 02:40 AM | #41 | |
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05-04-2013, 06:25 AM | #42 | ||
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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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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. Last edited by CanAutM3; 05-04-2013 at 07:13 AM.. |
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05-04-2013, 06:53 AM | #44 | ||
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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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