sparkplug indexing

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Magnetoman

Magnetoman

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vincenttwin said:
So I have one for towards the exhaust and the indexing washer web site says towards the inlet , So its in the middle for me ,I guess it makes sense not to hide the spark plug gap from the incoming charge, so gap pointing any where from inlet to exhaust should help.
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Beyond not having found a credible published study of the effect, if any, of indexing the plugs, remember that the valves are nearly half the bore diameter, so there are plausibility factors to consider. Saying the ground electrode should be pointed at, say, the inlet valve to mask the center of the plug still leaves a lot of the "unmasked" part of the plug pointed at the inlet valve. Since the mixture enters through all 360-deg. of the inlet valve, at best only that coming in through the area of the valve nearest the plug could conceivably be diverted in some way by the ground electrode.

But, the spark doesn't happen when the charge is rushing in. The inlet valve closes (the exhaust valve is already closed) and then the mixture is compressed by a lot before the spark finally happens. During this time the charge is free to continue move and/or change how it is moving within the chamber. Even without a deliberate squish band, the edge of the piston comes closer to the head than does the center. Because of this, it pushes mixture toward the center of the chamber as it rises. This motion imparted to the mixture is not a small effect, and it takes place after the valves could no longer be having any effect, but the arguments for indexing totally ignore it and only consider what might have happened relatively long ago, when the valve was open.

When the spark does happen the pressure rises to a very high level as the flame front ignites the mixture in the chamber. Except, through some mechanism that hasn't been explained, we are told that if the spark plug is "correctly" oriented there is an additional 1% h.p. The only way this can happen is if there is an additional 1% of fuel that otherwise didn't burn that now adds to the pressure rise. Since the combustion chamber is a sealed system, why would this 1% burn if the spark plug were pointed one way, but have managed to keep itself from burning if the plug were pointed in a different direction?
 
K

Kansas Bad Man

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You are wrong on several of your description's as to what is taking place in the combustion chamber . You have stated several times that you have not read of any creditable righting's as to the pluses on indexing. I have proved it to my self and re-laid my findings to the forum. YOU don't find them creatable so it would be like pissing in the wind to explain the FALSE description in your last post, its a shame you have a loyal fowling that believes .
 
Magnetoman

Magnetoman

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CollingsBob said:
It does seem to defy logic, however here is a link to a NGK sparkplug page...
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Ignoring the fact the text on the NGK site was written by someone from their marketing department, and taking it at face value, it says:

While most engines like the spark plug's gap open to the intake valve, there are still other combinations that make more power with the gap pointed toward the exhaust valve.
In any case, engines with indexed spark plugs will typically make only a few more horsepower, typically less than 1% of total engine output.

Yes, it does defy logic. Amongst all of this, the NGK site says it needs to be pointed toward the intake valve. However, Max says it needs to be pointed away from the intake valve to shield the electrode and provide a lean mixture which he says is need for easier starting even though the rest of the chamber is filled with a rich mixture for easier starting. But, the resolution of whether or not there is even an effect, let alone which direction the spark plug needs to face, comes down to the capabilities of dynos.

Dynos don't measure h.p. directly, but all measure some parameter that can be converted to h.p. by multiplying by a couple of constants. Ignoring that, let's say we have a dyno that directly reads out h.p. on an analog meter, and that it is designed for engines of 120 h.p. or less. In that case, there would be an analog meter running from 0 to 120, i.e. it would look just like the speedometer on a U.S. auto. Calibration to good overall accuracy isn't required for our dyno, only repeatable relative numbers numbers so we can determine the effect of changes we make. To see changes on our Vincent of less than 1% as the NGK page says we would have to discern from our analog meter run-to-run differences of the needle amounting to less than 0.5 when the needle was at 50. Think of a car speedometer and trying to determine if the speed changed by less than 0.5 mph at 50 mph from one run to the next up a long hill at a fixed throttle position as you indexed the plug from the inlet valve, to the exhaust valve, to halfway between. Now think of a Vincent engine at full throttle with vibration shaking everything in sight, and trying to determine if there was a difference of less than 0.5.

The Ford link is just to an article describing how to index. It doesn't provide anything new about whether or not it does any good.

Kansas Bad Man said:
You have stated several times that you have not read of any creditable righting's as to the pluses on indexing. I have proved it to my self and re-laid my findings to the forum.
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You've misread what I wrote. Several times I have referred to credible published studies by which I mean, for example, something in an SAE proceedings. This is not a reflection on you. But since it seems that if there is any effect at all it is at the 1% level, documented results of studies conducted according to accepted engineering standards are needed in order for a useful conclusion to come from this.
 
b'knighted

b'knighted

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[QUOTE=" Now think of a Vincent engine at full throttle with vibration shaking everything in sight, and trying to determine if there was a difference of less than 0.5.[/QUOTE]


How dare you - Vincents do NOT vibrate. I once had a six fifty Triumph so I do know what vibration is.
 
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