Re: Natural rev limiters

[bearbvd@domain.elided (Greg Hermann)]

>  The article included a photo of the piston and the connecting rod from
>one of the Ferrari engines.  The piston looked "odd" in that it had very
>little height to it.  By that I mean consider that a piston can being
>described as a "cylinder".  A cylinder
>can be defined as having a diameter "D" and a height "H".  A Borge piston
>for an Alfa has similar measurements for both "D" and "H".  The photo of
>the F1 piston had measurements where "D" >>"H" presumable because the
>stroke is so small and so as to
>reduce mass from the piston's head.

Oddly enough, I think that you might well find that the enormous V-8's
which are run in the "Pro-Stock" drag racing classes actually achieve
significantly greater maximum piston accelerations than the current F-I
engines do--but, of course, they do not do so for as long a period of
time---

They do not turn as many revs as the F-1 engines do, but their strokes are
orders of magnitude greater! The pistons in these critters do tend toward
the same sort of proportions as you describe for the F-1 pistons, though. I
believe that the Pro-Stock engines turn at least 8000 rpm, perhaps 10000 in
some cases, and many of them have strokes in excess of 5 inches!!!


>  Apparently these engines do not use mechanically actuated valves via
>camshafts but rather pneumatically actuated valves.  There's some sort of
>compressed air source used to open and close the intake and exhaust valves
>because it can be done more

It's pneumatic pressure instead of valve springs. The cams are still there,
doing all that they usually do.

>reliably than an engine using tappets, springs, and camshafts.  This setup
>also allows the engine to be run in a number of different configurations
>as there are no camshafts needing to be replaced to change lift, overlap,
>and duration....  just change
>the program and off you go.  BTW - I want one of these pneumatic valve heads!!!
>
There are two problems solved with pneumatic valve closure: fatigue of the
springs and heat build-up in the springs (due to hysteresis).

Greg

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