[Ducati] 17000 RPM MotoGP Limit?

[Scott Cloninger]

Current pneumatic valve seating systems overcome float by using a
pneumatic (nitrogen) spring rather than a mechanical (steel) spring.
The friction required to overcome that spring isn't eliminated, as a cam
and associated valve train (followers, pushrods, or what-have-you) are
still used to actuate the valves.  However, pneumatic valve return
allows for less compromise in closing rate versus seat pressure.
Mechanical springs must have high seat pressures (and hence high force
passed through the valve train to unseat them) in order to insure
appropriate valve closure rates.  Pneumatic valve return should allow
lower pressures at the valve seat whilst still maintaining a suitable
valve closure rate.  This difference should reduce friction in pneumatic
seated systems when compared to mechanical spring systems, but should
still be significantly greater than the friction losses generated in a
well tuned (and closer springless racing) desmodromic valve actuation
system.

No pump is required with this system, as it is a CLOSED system similar
those used in gas charged shock absorbers.  Gas (nitrogen) is just
shoved back and forth into an accumulator with each valve stroke.

Pneumatic actuation, however, is a whole other beast.  I don't doubt
you'll see pneumatic actuation in the next ten years, and that system
should make desmodromics obsolete. (or MORE obsolete, depending on your
current stance)  Pneumatic actuation would use a pumped gas (ostensibly
air) to both seat and unseat the valve, and should allow for infinitely
variable valve timing depending upon load, rpm, throttle position, etc.
This system would require no cams and would completely eliminate valve
train losses, but at the cost of pneumatic pumping losses.  The
magnitude of those losses would be determined by pressure and flow
requirements, and might be higher than valve train losses.  However, the
added power (especially at less than maximum rpm) might more than offset
the pumping losses.

Time will tell!

My two centavos,

Scott Cloninger, P.E., MBA
Engineering Manager
CEI Enterprises, Inc.
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