True definition of Knock

[Carl Summers]

Thank you Len,
       Finally someone with some real world experience explains it a little
better......no offense to anyone(please).....there are so many factors that
induce detonation and preignition.......fyi....the combustion chamber shape
and dome/dish shape drastically affects detonation as does high swirl vs rpm
and cyl filling height.....I have played with this extensively vs
compression ratio always trying to maintain as high a (static)compression
ratio as possible......I can go on forever about differing situations(cam
overlap,exhaust valve timing events, short turn entry angles vs rpm, etc
........all I can tell you is I have proven 1180 hp on pump gas with no
water injection.(yes, i have seen the claims of 1300+ on pump gas...been
there done that and more...works great on a dyno...doesn't live in the real
world)...intercooled/supercharged 8.3:1......but it took alot of effort in a
marine environment where it sits at 5600 rpm for very long times instead of
seconds as in a drag race or fun spurt......hth's
-Carl Summers
p.s. how about a 40' Hallett with twin 572's that went from Huntington to
Catalina in 16 minutes....takes longer to fly.....was alot of fun testing
though....hehehe

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-----Original Message-----
From: owner-gmecm at diy-efi.org [mailto:owner-gmecm at diy-efi.org]On Behalf
Of Len Sabatine
Sent: Tuesday, July 11, 2000 3:48 PM
To: gmecm at diy-efi.org
Subject: Re: True definition of Knock


   How About the " Low Octane " portion of the mix in the chamber igniting
before
  the piston reaches past dead stroke position , causing the piston skirt
to be "jammed"
  into the cylinder wall. The "rattle" is then transferred in to the
Cylinder case, the sensitivity
  would vary as to the physical construction of the cylinder case [block
casting] , water
  jacketing , cylinder wall core thickness , firing order and the
particular engine design's
  tendency to detonate. Add to this " which is the Hungry Hole " , the
cylinder most likely
to initiate detonation ignition response. Wonder Why there's so many
different KS locations
and sensitivity variants. The factory also factors in long term piston /
wall clearance etc,
into the  frequency response / programming.  Add a bit of oil into the
chamber and run the
lead to far BTDC should really get the pot boiling.  Then throw in all the
component damage.
While Mr. Smith's explanation is excellent , I believe it's a bit more
complex in total scope
though. Anyone is free to disagree .
Len

>Totally, self explainatory
>Grumpy
>
> > "Knocking occurs when a minute portion of the most volatile component of
> > gasoline reaches the cylinder a fraction of a second before the
principal
> > fuel charge, which is supposed to arrive at the instant the spark plug
> > fires.  When the more volatile fuel arrives early, the heat and
>compression
> > inside the cylinder cause it to ignite before the main charge, which in
>turn
> > causes the knocking you hear."
> >           --Bruce W. Smith, Auto World Weekly (July 18, 2000)
>
>
>---------------------------------------------------------------------------
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>

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