[Diy_efi] Spark Plug Projection into Combustion Chamber

[Adam Wade]

--- Neil.Poersch at mts.ca wrote:

> I am machining my motorcycle cylinder heads to add a
> second spark plug to
> the combustion chamber.   I am wondering if anyone
> has any recommendation
> as to how far the plug should project into the
> combustion chamber.    I
> have seen some installations which recess the plug
> in a shallow pocket
> (~0.1" deep....really not much more than a chamfered
> edge of the spark plug
> hole) in the roof of the combustion chamber.  This
> is supposedly to allow
> the ignition spark to start the flame in a protected
> area.
> Any comments from anyone?

My experience has been that the most reliable
combustion for best power and least chance of
detonation occurs as close as possible to the
geometric center of the combustion chamber.  IOW, the
closer you can get the spark source to the "middle"
distance between the piston crown and the combustion
chamber top (as measured from the spark plug hole
location), the better, as a general rule.  I'd use a
projecting-electrode plug if it can be used without
interfering with piston travel.

> Obligatory DIY_EFI content:   I will be using my
> DIY_EFI WB O2 meter to
> fine tune my AFR once I have completed the dual
> plugging project.
> Theoretically the engine should run on a leaner
> mixture than before.  This
> should be a good example of not tuning to a
> particular AFR but instead to
> the AFR that produces the best power.

My experience has been that residual O2 in an engine
that makes best power follows roughly the same curve
as the torque curve.  It would be awfully nice if we
could come up with a cheap CO sensor, since my
experience has been that residual CO is the best
indicator of a proper air/fuel mixture and ignition timing.

=====
| Adam Wade                       1990 Kwak Zephyr 550 (Daphne) |
|   http://y42.photos.yahoo.com/bc/espresso_doppio/lst?.dir=/   |
| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |

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