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From: (no name) (no email)
Date: Sat May 12 2007 - 22:47:43 EDT
Harry,
Here is what happens on one intake stroke of your 4 stroke Perk.
Exhaust valve closed. Intake valve open. Piston goes down with your hand over intake.
Basic Gas Law:
PV=nrT
Pressure times Volume is proportional to Temperature.
Assume no temp change (isothermic expansion) T is constant.
As volume increases (cylinder goes down) pressure MUST drop. You feel this on your hand (thus the warning of a hickey)
Now you have:
Pressure in ventilated crankcase 14.7 PSI.
Pressure in cylinder something less than 14.7 PSI
Delta P across the piston is forcing the piston back up against your hand. Connecting rod, crank, and starter are forcing the piston down thus increasing vacuum until it hits bottom of stroke.
I don't see how it can spin faster given a starter motor with a consistant HP output.
Same logic true with backpressure on exhaust.
This logic does not consider slip and leakage. At lower RPMs (like with your starter) slip starts to become a significant factor. But I still don't see how it could have spun faster with your hand restricting the intake.
Regards,
Wayne
Bermuda
Enterprise 54
King Harbor (South of LAX)
Los Angeles, CA USA
-----Original Message-----
From:
To: ;
Sent: Sat, 12 May 2007 9:26 AM
Subject: Re: T&T: Positive Displacement vs Dynamic Displacement
For may years now, I've put my palm over the intake of my Perkins 4-108 when
bleeding the injectors.
The engine spins several time as fast (with nothing to compress). I usually
get a black ring of
grease on my palm, but nothing more.
Harry
Mary Malcolm Cheoy Lee 40
On Sat, 12 May 2007 10:47:57 -0400, wabailey135 wrote
> Now to our situation, since our engines are positive displacement, I would say
that
> restricting mass flow through our engines (intake or exhaust) will cause your
engine to
> bog down faster than a 1 inch rode fouled on all 3 propeller blades.
>
> Thoughts?
>
> Regards,
>
> Wayne
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