Indexed Spark Plugs -- Nice...

[DracoFelis]

Originally Posted by Lug_Nut

I'm somewhat sceptical of the 'indexing' or rotating the plugs to align the electrode gap in one direction or another. If a given plug in a given hole is off by 330 degrees from the desired direction, and the plug is 'backed-out' by nearly a full turn,

Good point about the indexing washers affecting height of the plugs. However, IMHO the important thing is what does the various movements (both plug height movements and angle movements) do to the positioning of the spark?

And considering that we are talking at most a .064 inch height difference (i.e. at worst the thickness of the fattest index washer in the set), we clearly aren't affecting height much when we use the washers to index the plugs. OTOH when we don't index the plugs, the plug electrode could be at any angle at all, and thereby having the spark preferentially go out (from the plug) at any angle. As a result, it seems reasonable that plug angle (affected by indexing) is likely to have a much more dramatic effect on spark positioning than the minor height change caused by the index washers. If so, then indexing is still a net "win", even if/when you "lose something" do to changes in plug height.

Of course, we all know that plugs work "well enough" no matter how you position them. And that makes sense too, because as soon as you ignite the fuel/air mixture the ignited fuel will ignite fuel around it, and so on. So a spark anywhere in the fuel/air mixture (i.e. anywhere in the cylinder) should work.

The only issue then, is what (if any) gains (over more "random" plug positioning) can be had by adjusting where (in the cylinder) we put those sparks, and are those gains (if any) "worth it" from a cost/benefit standpoint. And on that level, I was able to find (using google) a number of reports/studies suggesting that spark position (i.e. "indexing" the plugs) does make a small but often noticeable difference in burn characteristics after you ignite the mixture (potentially affecting both FE and performance a small amount).

And since "indexing plugs" is cheap to do (maybe 5-10 minutes extra time when changing the plugs + the cost of a few index washers), I figured I would give it a try. And while the effect on FE (in my car) is still "up in the air", I have already noticed some (other) positive effects (mentioned in my previous post) in how the car drives. So it least in my car, I not only got an effect, but the effect was actually much more noticeable (to me) than I was expecting. i.e. I was expecting that indexing might help a very little (and was unlikely to "hurt" at all, even if it didn't help). However, what I got was several positive effects of the indexing, that turned out to be much more noticeable than I was expecting. Granted, each effect wasn't huge (and the car was running fine before the indexing, these were just bonuses/improvement), but considering how cheap indexing is, I really don't need a large benefit to justify the minor cost/hassle of doing it!

[GasSavers_Ryland]

if you look carfully at your spark plugs you will notice one side gets hotter then the other, or what looks almost like a shadow on the plug from the hot gasses, and from one side of the plug being cooler and leaving a very very small amount of soot on that cool side of the plug, you want the spark to be on that hot side I would think, right? either way, it's a strong enough theory that when you replace the spark plugs on the Honda Insight, that you have to check the indexing stamp on the head to tell what spark plug you need for that hole so the electrode lines up.