Re: C/W Cranks etc.

[WALTEE <WALTEE@prodigy.net>]

Melissa & Jim wrote:
> 
> On  1 Sep 97, Patrick Joel Morton wrote:
> 
> > At 00:46 3.1.1980, Toby Basiliko wrote:
> >
> >  * Huh?
> > 
> > 
> >
> 
> Much of what you say is clearly true:  Competition engines run to the
> limit will not last as long as conservatively driven engines.  OTOH,
> there is much here that I must take issue with.  A counterweighted
> crank (of any kind) has a larger moment of inertia than the stock
> crank, so, all other things being equal, it will take a bit longer to
> rev up.  In reality, I suspect the difference is unnoticable, but
> whatever effect there is, it is in the opposite direction than you
> imply.
> 
> There is no extra HP to be had from a CW crank, unless you count the
> HP that might otherwise be wasted in the flexing of the stock crank
> at high revs.  I don't know if you count beating up the center main
> bearing saddles in the case as wear, but I think it would be fair to
> do so.  At any rate, this is what the CW crank will help avoid.
> It was my understanding that the "horizontally opposed" cylinders were  at the crux of the biscuit. The two transversely opposed pistons are traveling to the end of their respective strokes simultaneously, sort of to cancel each other out, in a recipricating mass sort of way. This tends to make our crankshaft way perform a sort of snake dance as the pistons go from full stroke speed -to zero- and back to full speed as they go to BDC. I was under the impression that the CWC was only to lessen this snake dance, and save our friends, the bearings, from a premature death. But once again, there is the ugly spectre of moment of inertia being larger (lengthened, increased?) that makes the rev-up take longer, hence the lightened flywheel.
 
> I agree that a CW crank is not a performance item.  Rather it is a
> longevity item which allows you to run at higher revs withoud damage.
> It would also be fair to agree that the CW crank is pointless unless
> the rest of the rotating parts are also balanced properly.
> Lightening of certain components has performance benefits, but
> they also carry a durability cost.
This seems to be the reasoning behind, when you read about big buck
engines, they are
counterweighted+lightened+balanced+blueprinted+magnafluxed=$$$

> 
> I agree completely that all advertizing should be read with a
> jaundiced and critical eye.  My personal pet peeve is the selling of
> anything as "billet" when any machinist can tell you that if you are
> after strength and fatigue resistance you need to be looking at a
> forging.  Turning something from a billet is just a cheap way of
> doing low volume production.
If you look at a cross section of a forged part, the "grain" of the
metal follows the casting shape, whereas a billet piece has the grain
extending straight through, where the weakest point will be where the
grain extends to the edge of the shape, rather than following it.
> As to why VW didn't do this from the start I suspect that the answer
> is simply that VWs were for the masses and the enthusiasts were
> expected to drive Porsches (which came with CW cranks.)
Hear,hear. More power to the masses!
David Walters
'73  1600L Notch
S. FL, USA