Combustion chamber & twin plugs

[Shaun Brady]

At 10:18 PM 9/30/96 -0700, you wrote:
>Michael Fawke wrote:
> 
>Does anyone have any references to any work dealing with multiple
>spark plugs per cylinder?

The best data set I've seen is in a little pamphlet by Branch Heads (I think
it was Branch, "Flowmetrics",??) on developing a street Harley Davidson 1320
"Big Twin".

The Harley is the most pathetic thing you've ever seen from a performance
standpoint, a huge open hemispherical combustion chamber, big piston domes,
pushrods, an intake system that robs peter to pay paul, iron and air cooled
to boot.

They spent weeks of dyno time trying every popular performance cam, pipe,
carb, & head for the bike.  There is a pretty good narration that goes with
it on their rational.

The cliff notes version is that the dual plug mod is effective at improving
Hp and reducing the amount of ignition advance required for peak power.  The
caveat is that if one plug in the chamber fails, the timing will be too
retarded and you will smoke that poor air cooled motor before you know it.

The interesting thing is that when squish belts are added to either side of
the chamber, peak power occurs with spark advances similar to the 2 plug
head, and the dual plug mod no longer shows a performance benefit.

Edelbrock markets a head for Harleys that uses this style of combustion
chamber (and several port mods) that produce remarkable power gains.
Although if you want large delta's its best to start with low initial values.

Harleys are a long way from modern hot rods, but I think a lot of the data
applies to open chamber V-8s.  Vizard indicates that a closed chamber 9:1
350 chamber chevy 350 with dished pistons (to match the combustion chambers
- Banks calls them "reverse deflector) are worth 20 hp over a flat top open
chamber motor with the same cam.

$.02 more.

Shaun Brady