Interesting graph on plug orientation

[BLSTIC]

Not asking anything, just sharing something I found

So I was browsing for info on tumble and swirl and I came across this graph



The accompanying article can be found here

https://www.semanticscholar.org/paper/S ... 6753129610

And the text accompanying the graph was

A. Spark Plug Orientation and Effect on Lean Limit
Systematic experimentation by both Ziegler et al. [14] and Anderson and Asik [15] have shown a heavy influence on spark plug orientation to mean flow direction. Ziegler concluded that a crossflow orientation (figure 1) of the spark plug leads to the largest development of flame growth, as demonstrated in figure 2, and also the widest lean limit range. Anderson and Asik’s experiments appeared to mirror that or Ziegler, concluding that a 90◦ angle is more beneficial than a downstream orientation, additionally finding that ignition can be improved with a higher flow velocity over the spark plugs. Indeed, Nagayama et al. [18] showed how the misfire limit could be improved with the introduction of swirl. This section reviews the impact on rotating flows in the combustion chamber, pertaining particularly to flame propagation, spark plug considerations, lean limit and cycle-by-cycle variations.

So assuming you aren't indexing for clearance, it may be that indexing the plugs shows gains sometimes is not due to pointing the flame in the right/wrong spot, but because the plug is at some orientation to charge motion at firing time. It's worth noting that that graph (assuming 3000rpm) represents about 2 degrees of crank motion. It's also worth noting that unless you're 180 degrees out you're probably close enough. Either way next time I index plugs it will probably be on a 4v engine with zero swirl, so I've got an easy job of getting it right.

[jake197000]

Used to index plugs when I dragged and did quarter mile speed runs in big bore triple water cooled 2strokes,couldn't say it really did any anything.heasd were pretty much hemi heads.had data recorder.and kept excellent notes.

[Roy]

Dave Vizard has a very informational picture in one of his books about why this works. He was talking about spark plug modifications and the effect of swirl in the chamber on spark. I would post it but I don't want to upset him since it is his book. If the ground electrode is perpendicular to the airflow in the chamber then the spark becomes a LOT longer. In his picture he has a spark plug in a static environment showing the spark next to another picture with the same setup but with swirl simulated (probably used a blowgun or something since the picture was not in the chamber) the spark was blown sideways what looked to be an inch. It was an amazing thing to see.

[Warp Speed]

I have tested this theory, and didn't see any effect in either cylinder burn rate or output.
There might be some variables to consider, like chamber design and plug placement in the chamber but........

[GARY C]

Indexing plugs can show a major power gain... If they are being beat shut by the piston dome, the only thing I ever gained at the track indexing plugs was header burn.