the 2014 job should be a walk in the park for metal valve springs (ie timbo's suggestion seems good)xpensive wrote:Interesting thought, even if the hysteresis of conventional springs would mean a power-loss in itself, constant-pressure pneumatics don't have that problem. But how much, I have no idea, anyone?timbo wrote:I wonder, with a 15k rev limit, and possibly even less used because of limited fuel-flow, wouldn't it make sense to try conventional springs instead of pneumatics?
The cons are obvious -- resonances in springs were limiting the rev band up to 11k-12k, the pros are elimination of nitrogen supply bottle and possible simplification of valvetrain.
surely hysteresis has never been regarded as signicant or a problem in metal valve springs ?
excessive heating (from any source) of a metal valve spring must be undesirable, but is easy to deal with ?
hysteresis would be least what we classify as torsional strain (maybe Honda knew that when choosing torsion valve springs)
any material that has a clear and (relatively) long elastic range should have trivial hysteresis over a much of that range
that's what makes eg a good 'spring' grade of metal
most load cells are basically metal springs, and they make quantified claims of very low hysteresis eg 0.1%
(true, helped by selecting the hysteresis properties of the strain-sensing element to part-cancel hysteresis in the springs)
isn't hysteresis inherent in gas springs though ?
the difference between isothermal and adiabatic deflections in a gas spring represents the potential 'hysteresis' of a perfect gas ?
(though this has little effect at valve spring speeds ?)
and our gas springs are made from real gas, not perfect gas, and so have hysteresis effects from additional sources
equivalent and analagous behaviour does occur in even the best metal spring material, this impedes measurement of hysteresis
(my estimate from attempted practical investigation is around 0.2% hysteresis at valve spring levels of strain)
so what would 0.2% 'hysteresis' from whatever source do to a metal valve spring regarding cooling needs and power loss ??
and how could this be worse in those respects than a gas valve spring ??