Date: Wed, 29 Jan 1997 15:38:42 -0800
From: Mike West <mwest@cdsnet.net>
Subject: Re: Oil bath air filter / Paper Filter

>
>I fail to see how these things can work.  I've used oil bath air cleaners
>on Briggs and Stratton engines and on my grandfather's old pick-up - and
>they simply fail to impress me.  Sure, the oil does get dirty in time but
>how can you just pull air and "hope" that contaminates fall into the oil
>where as a paper filter will filter all the air that the engine recieves?
>
>Can someone explain to me the why, whats and ifs about these things?


  I don't want to even get into this but you have angered the V-dub
 Gods and will bring the wrath down on all of us.  :-(

 I don't want to get into it because it is a very complex piece of
Engineering and difficult (and long winded) to describe and justify.

 Ok, a centrifuge, if you aren't impressed with a v-dub air cleaner,
I will have to explain a centrifuge.

 A centriufuge works by spinning around little test tubes full of
"stuff" and seperating them into layers based on the weight of the
molecules in the solution.

 Blood tests use the centrifuge to determine what all is in your blood
before they jam you with a needle full of "other stuff" that will make
you well or kill you if they guess wrong.

So you better hope it works.

 Ever seen a cream seperator? Works the same way. The heavier molecules are
forced to the outside edge while the lighter cream is
seperated from the milk in the middle.

 Then there is the "Cyclone Seperator in a boiler that seperates the
water from the steam. Same principle.

 Newtons second law, I think.? "A body in motion resists any change in
motion or direction."  Something to that affect.

Also called "centrifugal" force, a misnomer, but useful in understanding or
explaining the phenomenon.

So, we have 2 or more substances in the same space.
One is air and one is a dust or worse. Also water.

The dirt/dust in the air weighs more than the air so it has a greater
resistance to a change in direction.

Bring this mixture up to a velocity and then change the direction of flow
real quick. The dirt will continue on it's original path while the air will
successfuly make the change in direction.

There are 2 changes in direction just getting the air from outside
the car to inside the air cleaner. Right angles both.

 Now we suck the air in a realatively small inlet at the end of a long
horn. Increase velocity and blend with warm air at the same time.
 The crankcase vent tube is also in there.

 Now it gets dumped into a big bowl around the carb intake.

Here is where the dirt and dust particles are thrown into the walls
and let drop down into the bottom and trapped in the oil.

Not satisfied yet, the Engineers make the air change direction 2 more
times.

Once to the bottom and close to the oil and then back up thru a tube
and then a reversal again for the entrance into the "Carb Majeur".

 Each time there is this change in direction there is more dirt removed.

I suppose I should cover the fact that the tube there in the center is
a calculated length and even if you take off the air cleaner you have
to put a "velocity stack" on the carb the same length.

I say "have to", you can leave it off but you will suffer great loss
in mileage.

 Now lets look at the paper filter. Not too bad in principle but a
bit light in all the factors and even in the area it does work in.

It is very possible to get a paper filter that will stop a smaller
particle than the "oil bath" job.

Problem is, as soon as it stops a particle, that hole in the paper is
now closed. It now will draw less air than before. Get it wet and it
plugs even more.

The oil-bath never restricts the air flow.

So if you change filters "Real" often, you might achieve a better
quality of air than the "oil bath" cleaner.

Can it pull 125 CFM unrestricted?

Will it also remove water like the stock one?

Now can you get one that has the crankcase vent at the proper vaccum
and the warm air inlet at the proper place and the fuel tank recirc.
vent in the proper place and a shut-off for the cold air that will
hook up to the Thermostat?

If you can then you're in the gold.

Even VW made a better filter, I might add. It was on the war machines
that were in Rommels "Desert Storm".

It was a "cyclone seperator" and the description I read said it seperated
the sand from the air and then dumped it in the exhaust pipe.
 More likely it used the exhaust for another increase in velocity.
 The "oil bath" cleaner was no doubt still in it's usual
place as a final "polisher" before the air entered the carb.

If you look at the "dune buggies" they put about a 15 gallon drum on
top and put filters back to back in them. Like, about six.

Of course they change them every day also.

Let's cover one more option, there is a "Liftime Turbo Air cleaner"
on the market for some major bucks.

You have to ask how it works? It emulates a VW stock air cleaner.

If you prefer "cute" to "ugly" you still aren't impressed.

Put something on there, I don't really want to rain on anybodies parade.

 Anyway, that's why I didn't want to get into it.  :-)

 west