[Diy_efi] Venturi effect crankcase breather

[Adam Wade]

--- Djfreggens at aol.com wrote:

> aeration doesnt occure form air being in the
> crankcase. aeration occure when the oil basically
> becomes low in viscosity and begins to have a low
> enough surface tension to contain a gas and become a
> bubble.

That sounds a little backwards to me.  You can contain
a bubble inside of anything, including a solid;
viscosity is not the issue.

My understanding of aeration is that it occurs from
oil being flung around, splashed, and so forth by
moving metal parts in the crankcase.  It's why we have
windage trays, and don't run the crank in the sump (of
course, there are the extremely high oil temperatures
and engine drag to think about there, also).

> lowering the pressure will only egxacerbate this
> problem.

So how come the engineers have found otherwise? 
Doesn't make sense to me.  You're saying the exact
opposite of the research I've seen.

> its not gonna be a perfect vacum

Of course not.  Blow-by always occurs; ring and seal
sealing are imprefect; and there will always be
evaporable fractions in the crankcase that will
vaporize at low pressures, thus raising pressure, or
at least slowing pressure drop.  As I'd already noted,
more than a fairly small drop in pressure will cause
damage to rings, cylinder walls, and of course ring
sealing.

> the gas sweeps by the oil film and it blows bubbles 
> havent you played with any kids bubble makers lately

Not that use motor oil, no.

To areate oil from moving air, you'd have to have air
moving at an extremely high speed to get it into the
oil, assuming you're talking aout air moving over the
surface of the oil in the sump.

I cannot prove it, but I think your belief about the
source of aeration is off the mark.

> as for reducing the boiling point of the oil this
> could very well cuase the airation your trying to
> stop by creating vapor.

Er, okay, color me confused.  Parts of the oil turn to
vapor, and are either sucked away by the low pressure
in the exhaust, or recondense into oil components.  I
see no problem there.

> as for the effectivness of such setups. yes the
> additional ring seal is nice. but opening teh second
> gap seems to really help the problem alot more.

Do you mean using a second ring with a wider gap in
it?  That doesn't make much sense to me.  You just
defeated the purpose of having the ring there in the
first place.

> the thing you are trying to releave is the boundry
> layer gases that bascially cuase ring fluter at high
> rpm.

And here I thought it was because of the resonant
frequency of the ring.  Silly me.

=====
| Adam Wade                       1990 Kwak Zephyr 550 (Daphne) |
| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |

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