Re: Natural rev limiters

[eric.schnettler@domain.elided]

I've just been reading through a number of AD's and came a cross the th=
read on "rev limiters" and what physical limitations there are on the s=
peed at which our wonderful Alfa engine's can turn.  This very subject =
has been reviewed approximately 3 months=20
ago in either "Road and Track" or "Car and Drive" in one of their contr=
ibuting editor's monthly columns.  (I can't recall which specific publi=
cation this appeared in right now but if anyone wants more information =
send your request to me off digest and=20
I'll dig up the articles.)=20
  In the writer (spelled something like "Cscear" though this is probabl=
y spelled wrong.. sorry) was reviewing the stellar performance of curre=
nt Formula One normally aspirated engines and had obtained a single pis=
ton from Ferrari's 1998 F1 engine.  In=20
the article, he addressed the relationships between horsepower, torque,=
 and RPM in engine design.  He highlighted the fact that the 1999 F1 en=
gines are capable of turning in excess of 17,000 RPM for sustained peri=
ods.  He also went into great detail=20
regarding the stroke and bore of the engines and that the engine design=
ers we able to extract more horsepower from the engines which utilized =
a very short stroke and dizzying crankshaft RPM's.  The basic physics o=
f engine performance is that Horsepower=20
or "Power" is a measure of energy per unit time where as "Torque" is in=
dependent of unit time.  The faster you can turn the crankshaft the mor=
e reactants the engine can consume in a given period of time and the mo=
re horsepower it can generate.  The=20
Ferrari engine (and presumably the other team's engines) have to use ex=
otic materials like titanium, ceramics, and metal matrix's to enable th=
em to turn at these rates without flying apart.  The author's article d=
iscusses in detail the forces experienced=20
by the piston during each revolution of the crankshaft.  The piston ess=
entially is "at rest" or motionless at top dead center and at bottom de=
ad center and it is accelerated from rest to some maximum velocity and =
then decelerated back to zero velocity=20
twice per crankshaft revolution.  According to the author, the accelera=
tion experienced by the piston in these engines are on the order of 100=
G's.
  The article included a photo of the piston and the connecting rod fro=
m one of the Ferrari engines.  The piston looked "odd" in that it had v=
ery little height to it.  By that I mean consider that a piston can bei=
ng described as a "cylinder".  A cylinder=20
can be defined as having a diameter "D" and a height "H".  A Borge pist=
on for an Alfa has similar measurements for both "D" and "H".  The phot=
o of the F1 piston had measurements where "D" >>"H" presumable because =
the stroke is so small and so as to=20
reduce mass from the piston's head.
  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=20
reliably than an engine using tappets, springs, and camshafts.  This se=
tup also allows the engine to be run in a number of different configura=
tions as there are no camshafts needing to be replaced to change lift, =
overlap, and duration....  just change=20
the program and off you go.  BTW - I want one of these pneumatic valve =
heads!!!

Enough of this for now as I've developed diarrhea of the keyboard.
It's pretty amazing technology that is being used in today's high perfo=
rmance F1 engines.

Best Regards,
Eric Schnettler
Manlius, NY=20

88 Graduate - Engine and Tranny to be pulled next weekend.

snip

>DOHC system can handle very high rpm (my motorcycle's redline is at 12=
,000rpm).
>IMO the problem  isn't the RPM value itself, but SPEED of piston......=
=

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