--===============5875442505861053193==
--00000000000092dcbb05ec5a3c4a
I think you are absolutely correct Bob.
M
On Mon., Oct. 31, 2022, 3:56 p.m. Bob Spidell, <bspidell@comcast.net> wrote:
> I think it's the difference between reading pressure/vacuum at the
> crankcase (dipstick tube) vs. pressure/vacuum at the intake manifold (where
> a typical vacuum gauge is mounted). PCV valves close under vacuum at the
> intake (small) side and open when the vacuum decreases--at part throttle or
> WOT--where the 'leak' is less consequential. High neg. pressure, at idle
> and overrun, at the intake side closes the valve--at least partially, they
> all seem to 'leak' some--else you'd have a massive intake leak. Hence
> little or no vacuum in the crankcase at overrun. At idle, the low BMP makes
> the blow-by less of an issue.
>
> As always, I stand ready to be corrected.
>
>
>
> On 10/31/2022 11:48 AM, Michael Salter wrote:
>
> I think there is something to what you suggest Bob but, when I first
> observed the only very minor negative pressure on overrun I was somewhat
> confused because my thinking was that as there is minimal blow-by on
> overrun the PCV valve (vacuum source) should have encountered no problems
> keeping the crankcase evacuated. Further study however has provided what
> may be an explanation.
> Apparently the PCV valve selected, and this applies to most versions,
> actually throttles down the air flow at high vacuum aka overrun.
> I suspect that I was observing the results of this on the manometer.
> Closing off the original valve cover breather tube probably meant that
> crankcase pressure dropped further because there was less "make up" air
> available during these conditions.
>
> M
>
> On Mon., Oct. 31, 2022, 2:26 p.m. Bob Spidell, <bspidell@comcast.net>
> wrote:
>
>> Michael,
>>
>> From your blog post:
>>
>> "occasionally on overrun very little if any negative pressure was evident
>> in the crankcase so, in order to improve things a little I installed a plug
>> in the hose which runs from the valve cover to the rear air filter and this
>> resulted in a significant improvement"
>>
>> Probably because you're pulling air (and sump oil) into the crankcase
>> through the rear main 'scroll' seal (and dipstick tube and oil filler cap
>> hole). This is how the typical, owner-installed PCV installation on the
>> 6-cyl cars functions as the PCV valve meters gasses both from the crankcase
>> and the valve cover. But ... with fresh, filtered air coming in from the
>> carb air filter you essentially had a true PCV 'system,' where the
>> gasses--fresh air and blowby--are cycled back into the intake manifold to
>> be burned in the cylinders.
>>
>>
>> [image: Video: The Importance Of Using A Catch Can System]
>>
>> On 10/30/2022 10:22 AM, Michael Salter wrote:
>>
>>
>>
>> Sorry forgot the link...
>>
>> Adding a PCV to a 100.
>>
>> https://precisionsportscar.com/austin-healey-100-pcv-system/
>>
>>
>>
>
--00000000000092dcbb05ec5a3c4a
Content-Transfer-Encoding: quoted-printable
<div dir=3D"auto">I think you are absolutely correct Bob.<div dir=3D"auto">=
<br></div><div dir=3D"auto">M</div></div><br><div class=3D"gmail_quote"><di=
v dir=3D"ltr" class=3D"gmail_attr">On Mon., Oct. 31, 2022, 3:56 p.m. Bob Sp=
idell, <<a href=3D"mailto:bspidell@comcast.net";>bspidell@comcast.net</a>=
> wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 =
0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
=20
=20
=20
<div>
I think it's the difference between reading pressure/vacuum at the
crankcase (dipstick tube) vs. pressure/vacuum at the intake manifold
(where a typical vacuum gauge is mounted). PCV valves close under
vacuum at the intake (small) side and open when the vacuum
decreases--at part throttle or WOT--where the 'leak' is less
consequential. High neg. pressure, at idle and overrun, at the
intake side closes the valve--at least partially, they all seem to
'leak' some--else you'd have a massive intake leak. Hence l=
ittle or
no vacuum in the crankcase at overrun. At idle, the low BMP makes
the blow-by less of an issue.<br>
<br>
As always, I stand ready to be corrected.<br>
=C2=A0<br>
<br>
<br>
<div>On 10/31/2022 11:48 AM, Michael Salter
wrote:<br>
</div>
<blockquote type=3D"cite">
=20
<div dir=3D"auto">I think there is something to what you suggest Bob
but, when I first observed the only very minor negative pressure
on overrun I=C2=A0 was somewhat confused because my thinking was th=
at
as there is minimal blow-by on overrun the PCV valve (vacuum
source) should have encountered no problems keeping the
crankcase evacuated. Further study however has provided what may
be an explanation.=C2=A0
<div dir=3D"auto">Apparently the PCV valve selected, and this
applies to most versions, actually throttles down the air flow
at high vacuum aka overrun.=C2=A0</div>
<div dir=3D"auto">I suspect that I was observing the results of
this on the manometer.=C2=A0=C2=A0</div>
<div dir=3D"auto">Closing off the original valve cover breather
tube probably meant that crankcase pressure dropped further
because there was less "make up" air available during t=
hese
conditions.</div>
<div dir=3D"auto"><br>
</div>
<div dir=3D"auto">M</div>
</div>
<br>
<div class=3D"gmail_quote">
<div dir=3D"ltr" class=3D"gmail_attr">On Mon., Oct. 31, 2022, 2:26
p.m. Bob Spidell, <<a href=3D"mailto:bspidell@comcast.net"; tar=
get=3D"_blank" rel=3D"noreferrer">bspidell@comcast.net</a>>
wrote:<br>
</div>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border=
-left:1px #ccc solid;padding-left:1ex">
<div> Michael,<br>
<br>
From your blog post: <br>
<br>
"occasionally on overrun very little if any negative
pressure was evident in the crankcase so, in order to
improve things a little I installed a plug in the hose which
runs from the valve cover to the rear air filter and this
resulted in a significant improvement"<br>
<br>
Probably because you're pulling air (and sump oil) into the
crankcase through the rear main 'scroll' seal (and dips=
tick
tube and oil filler cap hole). This is how the typical,
owner-installed PCV installation on the 6-cyl cars functions
as the PCV valve meters gasses both from the crankcase and
the valve cover. But ... with fresh, filtered air coming in
from the carb air filter you essentially had a true PCV
'system,' where the gasses--fresh air and blowby--are c=
ycled
back into the intake manifold to be burned in the cylinders.
<br>
<br>
<br>
<img src=3D"https://www.speednik.com/files/2016/06/2016-06-15_1=
8-14-25.jpg" alt=3D"Video: The Importance Of Using A Catch Can System" styl=
e=3D"width:583px;height:388.667px;margin:0px"><br>
<br>
<div>On 10/30/2022 10:22 AM, Michael Salter wrote:<br>
</div>
<blockquote type=3D"cite">
<div dir=3D"ltr">
<div class=3D"gmail_default" style=3D"font-family:arial,san=
s-serif;font-size:small"><br>
</div>
<div class=3D"gmail_quote"><br>
<div style=3D"font-family:arial,sans-serif;font-size:smal=
l" class=3D"gmail_default">Sorry forgot the link...</div>
<br>
<div dir=3D"ltr">
<div style=3D"font-family:arial,sans-serif;font-size:sm=
all">Adding
a PCV to a 100.</div>
<div style=3D"font-family:arial,sans-serif;font-size:sm=
all"><br>
</div>
<div style=3D"font-family:arial,sans-serif;font-size:sm=
all">
<div style=3D"font-family:arial,sans-serif;font-size:=
small" class=3D"gmail_default"><a href=3D"https://precisionsportscar.com/au=
stin-healey-100-pcv-system/" rel=3D"noreferrer noreferrer" target=3D"_blank=
">https://precisionsportscar.com/austin-healey-100-pcv-system/</a></div>
<br>
</div>
</div>
</div>
</div>
<br>
</blockquote>
</div>
</blockquote>
</div>
</blockquote>
<br>
</div>
</blockquote></div>
--00000000000092dcbb05ec5a3c4a--
--===============5875442505861053193==
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
_______________________________________________
Archive: http://www.team.net/pipermail/healeys
http://autox.team.net/archive/healeys
Healeys@autox.team.net
http://autox.team.net/mailman/listinfo/healeys
--===============5875442505861053193==--
|