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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/
>
>
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Content-Transfer-Encoding: quoted-printable
<div dir=3D"auto">I think there is something to what you suggest Bob but, w=
hen I first observed the only very minor negative pressure on overrun I=C2=
=A0 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 provid=
ed what may be an explanation.=C2=A0<div dir=3D"auto">Apparently the PCV va=
lve selected, and this applies to most versions, actually throttles down th=
e air flow at high vacuum aka overrun.=C2=A0</div><div dir=3D"auto">I suspe=
ct 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 pr=
obably meant that crankcase pressure dropped further because there was less=
"make up" air available during these 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";>bspidell@comca=
st.net</a>> wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"m=
argin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
=20
=20
=20
<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 dipstick tub=
e 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 ai=
r and
blowby--are cycled 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_18-14-25.=
jpg" alt=3D"Video: The Importance Of Using A Catch
Can System" style=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">
=20
<div dir=3D"ltr">
<div class=3D"gmail_default" style=3D"font-family:arial,sans-serif;=
font-size:small"><br>
</div>
<div class=3D"gmail_quote"><br>
<div style=3D"font-family:arial,sans-serif;font-size:small" class=
=3D"gmail_default">Sorry forgot the link...</div>
<br>
<div dir=3D"ltr">
<div style=3D"font-family:arial,sans-serif;font-size:small">Add=
ing
a PCV to a 100.</div>
<div style=3D"font-family:arial,sans-serif;font-size:small"><br=
>
</div>
<div style=3D"font-family:arial,sans-serif;font-size:small">
<div style=3D"font-family:arial,sans-serif;font-size:small" c=
lass=3D"gmail_default"><a href=3D"https://precisionsportscar.com/austin-hea=
ley-100-pcv-system/" target=3D"_blank" rel=3D"noreferrer">https://precision=
sportscar.com/austin-healey-100-pcv-system/</a></div>
<br>
</div>
</div>
</div>
</div>
<br>
<fieldset></fieldset>
<pre>_______________________________________________
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