Date:         Thu, 4 May 2006 03:06:07 -0400
Reply-To:     "Daniel L. Katz" <katzd54@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "Daniel L. Katz" <katzd54@YAHOO.COM>
Subject:      Re: idle and black tower

On Wed, 3 May 2006 00:49:45 -0400, Daniel L. Katz <katzd54@YAHOO.COM>
wrote:

list:

recent post generated a fair amount of interest, and i'll just respond
briefly here instead of by pmail(s).

1. yes, i will endeavor to post pictures. not quite sure how to do that,
but sounds like time to learn, and i do have a digital camera. please give
me several days.

1a. on passenger side of intake manifold is port for auxiliary air
regulator hose. i use that port to access manifold vacuum, and, for now at
least, have taken auxiliary air system out of the picture entirely.

2. theory is that in steady state blow-by has to exit crankcase as fast as
it is produced. with this constraint, pressure will build in crankcase
until this steady state condition is satisfied - one way or another -
through hoses, past seals, whatever it has to do. if hose carrying blow-by
exhausts into usual intake port, then crankcase pressure has to be much
higher than if hose exhausts into intake manifold vacuum; engines with
lots of wear probably have more than usual blow-by, thus resulting in
higher crankcase pressures, especially with throttle closed (idle), and
possibly a buildup of blow-by pressure just above throttle, interfering
with normal intake of fresh air.

3. pcv valves are essentially one way valves, like check valves, except
that they partially shut off in the forward direction if the forward
pressure difference across the valve is great enough (idle). in a car with
true pcv (positive crankcase ventillation), the engine is essentially
vented to the atmosphere, and when the pcv valve partially closes at high
manifold vacuum, thus preserving high manifold vacuum and optimizing
idle, there is no danger of excessive blow-by pressure damaging engine.
normally, fresh air actually flows into the crankcase, which is kept below
atmospheric pressure via connection of pcv valve to manifold vacuum. the
vanagon 1.9 l, however, is not vented, and so, just staying on the safe
side with a high blow-by situation, being very conservative, i slightly
crimped the pintle end of the pcv metal housing to provide a stop, and
prevent the pintle from moving past full open - but valve still closes to
reverse flow (as in front-fire), and action is normal up to full open stop
(ideal for cruising).

3. although a true pcv system would be better yet, given modification
should efficiently clear crankcase of blow-by, thereby extending oil
lifetime and reducing sludge and varnish. reducing crankcase pressure also
means less wind resistance for moving pistons, and avoiding damage to
seals and other oil control problems if blow-by is unusually high.

4. since the steady state flow of blow-by is fixed, it might seem
unnecessary, actually counterproductive, to include a pcv valve, which
surely raises crankcase pressures a bit. in fact, the modification works
ok without the valve. but in the real world there are complications, and
the valve seems to damp out feedback effects which otherwise cause a less
steady idle. in addition, the pvc acts as an extra  baffle to help keep
oil drops from making the trip to manifold vacuum with the now fast moving
but rarified blow-by gases. also, the pcv valve stops reverse flow, and
therefore is a good safety feature in case of a front-fire.

dan

>list:

>modification worked wonders for '84 idle, overall running, and power. here
>is the current iteration:
>
>from exit of black tower:
>
>short 3/4" heater hose inside of which is pushed (snug fit) a modified pcv
>valve**, pintle side away from tower
>
>3/4" to 5/8" reducer (would use 3/4 to 1/2 inch if i had one handy)
>
>length of 1/2" hose making loop back and around toward intake maifold
>
>short molded 1/2" hose at manifold removed and replaced by short straight
>piece followed by original "y"
>
>connected looped 1/2" hose and also vacuum line for charcol canister
>to "y" (i had to extend line for charcol canister slightly, using ordinary
>rubber vacuum hose)
>
>i left the auxiliary air regulator out of the system for now. if future
>problems, it can be integrated with a "t" fitting, although it is pretty
>tight in there.
>
>the two intake ports, from auxiliary air regulator and original 3/4" hose
>from black tower, are plugged.
>
>i adjusted the idle control screw (really an air bypass) all the way in,
>and trimmed the idle/O2 sensor output using the co adjusting screw
>
>end results:
>
>approximately 880 +/- 30 rpm idle; O2 output .55 +/- .15 V
>
>added bennefit: certainly lower crankcase pressures and therefore LESS
>danger to seals from blow-by pressure.
>
>**throttling blow-by through pcv valve yielded a more stable idle than
>wide open operation, and probably helps with oil control as well (no blue
>smoke).  additionally, the pcv valve will close in response to a front-
>fire propogating back toward the black tower, thus protecting against a
>possible crankcase explosion (less of a danger here than in a true pcv
>system due to relative lack of oxygen).
>
>pcv valve was modified by slightly crimping the housing on the pintle end
>to prevent the pintle from moving past point of maximum open, thus
>avoiding the possibility of valve closing too much at high manifold
>vacuum, which would cause blow-by pressure to build up in the unvented
>crankcase (which could cause oil to rise up dip stick tube, perhaps blow
>seals, and etc). pcv valve action is otherwise normal.
>
>dan