Quote:
Originally Posted by mkoesel
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.
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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.