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Multi electrode Spark PlugSometimes, while searching for the next big boost in performance, efficiency, reliability, or any combination of these, we are willing to look into the more exotic and contested technologies that are popping up all around us. However, before sinking lots of time or money into a new product, it's important to see if the concept itself even holds water.

Years ago when I was selling auto parts, the big new thing was this gnarly-looking 4 electrode spark plug. This product promised everything from lower fuel consumption to better breathing. I didn't think twice about it until some of my customers began telling me that the plugs did nothing for them. This got me to thinking: what's so special about these plugs? In order to understand what might make these plugs different, it's important to know the basis of a spark plug's function.

The novelty of the 4 electrode plug wears down a bit

An ignition coil acts as a transformer that steps up the (typical) 12 volts from your car's electrical system to as much as 50,000 volts. When it's time to fire, the computer (or contact breaker) will cause the field to collapse in the coil, forming this tremendous voltage at the secondary side, connected to the center electrode of the spark plug. For a tiny fraction of a second, this huge voltage sits on the center electrode and causes the air in between the center and ground electrodes to ionize, or align themselves electrically. In a manner of speaking, it scares the air into forming a path between the two electrodes so that the current can jump.

Of course, we know from our elementary school days that any kind of potential energy will take the path of least resistance in order to relieve itself (think, finding the closest bathroom). Thus, it becomes clear that there really is no way that a spark will jump across to all four electrodes at once, as the pretty illustrations suggest. Once we understand this, the novelty of the 4 electrode plug wears down a bit- it will function just like a regular plug.

BoschPlugBottomViewHowever, there are two more considerations.

1. It is possible that the high heat from the spark jumping the gap would temporarily heat the chosen ground electrode more than the others. If this is the case, it is conceivably possible that this increase in heat will increase the impedance (or resistance) of that particular grounding path. Then it is possible that at the next spark event, one of the other ground electrodes makes an easier path, and is used instead. I can't really picture any advantage to this configuration other than marginally longer life of the plug, since each ground electrode is used less (the ground electrodes are, however, smaller on these plugs, so this will probably wash out anyway).

2. Some OEMs suggest or even require multi-electrode spark plugs, my best friend's 2001 4Runner, for example. I'm not positive as to why these plugs were mandated by the manufacturer- more than likely it is longevity related. However, I am a huge proponent of following your manufacturer's suggested maintenance procedures, and would not hesitate to install these plugs (based on millions of dollars of research by the manufacturer).

Bottom line: if your car had them from factory, or if they are suggested in your vehicle's maintenance literature, by all means use them. But as to whether or not they will give you any performance increase in your old, primitive electronic ignition vehicle (like my Mercedes 300E), I wouldn't bet the farm on it.

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Dan BullmoreDan Bullmore is a physicist and engineer from Houston, TX. Preferring the old to the new, Dan has owned many examples of Mercedes and Volvos and has devoted much of his time to maintaining and understanding them.


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Written by :
Dan Bullmore

Dan Bullmore is a physicist and engineer from Houston, TX. Preferring the old to the new, Dan has owned many examples of Mercedes and Volvo vehicles and has devoted much of his time to maintaining and understanding them.


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