[Healeys] Fwd: New post on my blog

[Michael Salter]

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 at 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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