Part 2: Reading Plugs, pistons, and valves (with Pics)

[Len Sabatine]

   Ok , just add the chamber cc variable to "ALL" the rest built in to a 
stock street engine.
   The end result is 1 rolling variable anyway, no big deal. It should be 
very obvious that
   there's no magic program to handle all of the variables + the ones we 
add. Just making
   an attempt to point this up , that's all !  Close enough qualifies when 
nothing else is. IMO
     Len

>One full turn on a 14mm sparkplug represents
>a change in combustion chamber volume of
>0.7*0.7*3.14*0.12 = 0.18 cc
>For a 58cc nominal chamber this is a net
>change of 0.31%.
>Are the ports matched to 0.31%?
>Intake manifold?
>The head temperatures?
>The injectors?
>What about the leakdown of each individual cylinder?
>
>A variation of deck height between cylinders of more than
>0.0009 inch has more effect on combustion chamber volume than one
>turn of the sparkplug.
>
>Are the rod center lengths (on a 5.7 inch rod!) accurate to
>this tolerance? What about the pistons and the crank throws?
>Is the block decked to this kind of tolerance? Is the crank
>that straight?
>
>With very, very careful technique you might be able to measure
>a difference of 0.18 cc in combustion chamber volume, but I think
>it is pointless -- other components that drive combustion efficiency
>vary much more than this.
>
>I agree with Bruce -- index your plugs for optimum placement
>of the ground electrode and initial flame-front travel.
>Don't worry about the variation in chamber volume of
>moving the sparkplug up or down..
>
>----- Original Message -----
>From: "Bruce Plecan" <nacelp at bright.net>
>To: <gmecm at diy-efi.org>
>Sent: Sunday, December 03, 2000 9:46 AM
>Subject: Re: Part 2: Reading Plugs, pistons, and valves (with Pics)
>
>
> >
> > I'm talking about a street car, not many are running cc'd heads.
> > Heck the we can start worring about the specific gravity of the fuel.  The
> > actual O2 content of the immediate air supply, etc.
> > There is a practical point to me, where you just take your lumps and go
>on.
> > If really worried about the volume of the heads then need to run water
> > injection about full time to keep any carbon deposits from collecting.
> > The thick spacer is what .020", racing a plug that much (or less) isn't an
> > amount I'd worry about in a street car.
> > In a spec. class or when the budget, time, money allows, but so many tune
> > ups are so far off that seeing that difference is not a big issue in my
> > book, IMO
> > Bruce
> >
> >
> >
> >
> > From: "Len Sabatine" <sabatine at epix.net>
> > >   The seat washers that make indexing  proceed faster also increases
> > > chamber cc's
> > >   in the specific Cyl, versus  stepping Thru numerous plugs to get the
> > > index on the $. The Nitty gritty.
> > >   The seat washers don't cut it, after investing hours to get the
>chamber
> > > cc's balanced. Ok if having
> > >   the chambers vary doesn't matter , It would to me!
> > >   Len
> >
> > > >Ahh, got what ya mean.
> > > >think it's Jegs has a plate with a plug tapped hole in it.
> > > >Then you can scribe a line to show where cylinder lines up per plug,
> > > >supposedly for faster indexing.
> > > >Me, I gota couple 3 packs of shims, a mike, and a magic marker (ie
>cheap)
> > > >Bruce
> > > >
> > > >
> > > > > Oh definetly not the place for indexing.. the serious drag guys
>obsess
> > > >over
> > > > > that level of detail (I've read).
> > > > >
> > > > > I thought the detail would be interesting. While the heads are off
> > though
> > > > > its good to screw the plugs in and see where they end up, depthwise.
> > > > >
> > > > >
> > > > > ----- Original Message -----
> > > > > From: Bruce Plecan <nacelp at bright.net>
> > > > > To: <gmecm at diy-efi.org>
> > > > > Sent: Saturday, December 02, 2000 7:19 PM
> > > > > Subject: Re: Part 2: Reading Plugs, pistons, and valves (with Pics)
> > > > >
> > > > >
> > > > > >
> > > > > > In anything on the street indexing really isn't a HP issue, IMO.
> > > > > > I does give ALOT more uniform plug readings.
> > > > > > The side electrode when positioned just right in a SBC can mask
>the
> > burn
> > > > > > pattern for 1/2 the plug.
> > > > > > Plugs should be in and out often enough that there is no carbon
> > **build
> > > > > up**
> > > > > > on the exposed threads.  Also, if the head sees and anti-seize
>from
> > time
> > > > > to
> > > > > > time treats the plug enough for it not to stick with AL heads.
>I've
> > > >even
> > > > > > been known to use a little AS on iron headed engines where the
>plugs
> > are
> > > > > > changed alot
> > > > > >
> > > > > > Also, be advised, AS is an insulator, and when used in excess can
> > cause
> > > >a
> > > > > > miss
> > > > > > Bruce
> > > > > >
> > > > > >
> > > > > >
> > > > > > > The only thing I have to contribute is that I've read that the
> > plug
> > > >base
> > > > > > > should be exactly flush with the lowest point of the comb
>chamber
> > > >entry.
> > > > > > ie
> > > > > > > there should be no 'thread pit' for carbon to collect in
> > regardless of
> > > > > how
> > > > > > > much male plug threading is exposed on the 'thin side' of the
>plug
> > > >hole.
> > > > > > > Indexing with spacers without considering this leaves
>compeditors
> > who
> > > > > have
> > > > > > > indexed thru plug selection (buy 200, find the ones that thread
>in
> > > > > PERFECT
> > > > > > > indexed position, sell the rest) with an advantage, however
>small.
> > > > > > >
> > > > > > >
> > > > > > > ----- Original Message -----
> > > > > > > From: Shannen Durphey <shannen at grolen.com>
> > > > > > > To: <gmecm at diy-efi.org>
> > > > > > > Sent: Saturday, December 02, 2000 5:51 PM
> > > > > > > Subject: Re: Part 2: Reading Plugs, pistons, and valves (with
> > Pics)
> > > > > > >
> > > > > > >
> > > > > > > > I see a problem.  Piston 2 is in the wrong spot!  It should
> > never be
> > > > > > > > between 2 others in a sb chebbie... : )
> > > > > > > > Shannen
> > > > > > > >
> > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> >
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