Quote:
Originally Posted by Inge_F
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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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.