Kozy wrote:MPS is a limit all engines are pretty much fixed by. It's actually more to do with the engines ability to breathe, than any mechanical properties sounding stesses within the parts. Above 25m/s, the inlet port velocities will tend to approach the mach index of 0.6, which is where they start to choke. .......
IMO not so
recent F1 engines have had uniquely high bore:stroke ratios (they have nearly doubled in 20 years)
similarly, however you look at it, their valve area is relatively much higher than ever before
eg Cosworth said of their engines pre V10 relative to later engines (that the later engines had about 35% lower gas velocities)
consider that they designed for and achieved max power at 21000 rpm (with variable trumpets)
check MPS at 21000 rpm
at lower rpm the low port velocities are helped by the 7 speed superfast paddle shifts and mapping to smooth the torque/rpm
often (ie in slowish corners) F1 can't use a decent torque curve so doesn't need one, ie it only needs a smooth torque curve
with conventional b:s ratios the piston speed is a reasonable indicator of port choking (though why not use gas velocities ?)
with recent mind-boggling extreme NA F1 b:s ratios it is not
conventionally, car engines are designed to be near choking (to help the power band), it's disadvantageous to avoid it
extreme NA F1 b:s ratio is further from choking because the piston acceleration-related stresses limit rpm to 21000
if MPS was the limiting factor they could run at eg 26000 rpm and this would give choking
over 100 years ago the GP Peugeot made extremely low b:s ratios compellingly fashionable
these were descended from vouiturette classes based on the road tax regime allowing more displacement to low b:s ratio engines
eg the dominant Lion-Peugeot, an 80 mm bore, 280 mm stroke V twin
these had extremely high MPS (again an exampe of the piston acceleration not the MPS dictating the safe rpm)
