"My understanding is that platinum is added to the centre pin to reduce corrosion of the centrepin, giving longer life. There is no other real advantage to it."
True, there is one small other advantage - since the platinum/iridium is more durable, it can be made smaller into a sharp point and not wear away as a conventional metal made into a sharp point would. Sharp points and edges ionize the air well and make it easier for a spark to be created and jump the gap, giving opportunity to increase the gap and still have less/no misfires.
Remember the AC Rapidfires introduced in the early 90's? These were conventional plugs designed for "better performance". They incorporated a "splined" center electrode (more sharp edges) and a "clipped" ground electrode (tapered to a point) that shrouded less - all concepts based on this discussion.
"I agree that 4 prongs aren't likely to give a 4 point spark, but it is conceivable that in the swirling gases of a combustion chamber the spark may be drawn away from one point to a neighbouring point. "
It's more than not likely, it's impossible. The spark will always go the path of least resistance, and only 1 of the prongs will be that path per spark event. So for a given spark event, only 1 of the prongs will get the spark. However, it's likely on the next event another prong will be the least resistive path if all 4 prongs are fairly equal in resistivity (which when new would be the case). Obviously spark events occur faster than the naked eye or normal camera/video shutter speed can distinguish, giving the illusion of multiple sparks simultaneously to all 4 prongs and those nice marketing photos.
I seriously doubt if the swirling gases have any effect on drawing spark away from one prong to another but I won't state that absolutely. Amclaussen's posts really hit the nail on the head.
My understanding is that platinum is added to the centre pin to reduce corrosion of the centrepin, giving longer life. There is no other real advantage to it. The platinum may be alloyed with the base metal as plating may not be a very rugged solution. The cost reductions likely come from highly mechanised production in China rather than reduced platinum.
I agree that 4 prongs aren't likely to give a 4 point spark, but it is conceivable that in the swirling gases of a combustion chamber the spark may be drawn away from one point to a neighbouring point. What impact that has on combustion I can only guess. The testing done by amclaussen suggests it isn't positive.
While the spark plugs were indeed bad, the 1000$ 'loss' is something you need to blame yourself for. You should have found the cause of the issue first before replacing a part that you merely suspected. I'm not saying it wasn't plausible, but before spending that much money I'd have triple checked everything.
I was talking about the four conventional ground electrode design, which was being promoted here recently.
Anyway, regarding best plug design for power in race modified street engines, racers have pretty well stablished the projected nose, conventional sparkplug is slightly better probably because it places the spark kernel closest to the sweet spot, usuallly located towards the center of the combustion chamber in most engines (provided it is usable in the combustion chamber used, and probably indexed to avoid being hit by the domed piston and to avoid the shrouding effect). If the sparkplug locates the spark closer to the chamber wall, it reduces overall efficiency, in other words, side firing and surface discharge plug designs are used to best advantage in engines with very close piston top to chamber distances (no conventional ground electrode can be used in those engines, and the efficiency is kept high in those conditions because of the extremely high turbulence resulting from very high compression ratios and RPM's, not at all the conditions of daily drivers ).
My gripe is that actually the spark can only jump to the nearest ground electrode, and given manufacturing tolerances for plugs, the second (or third, or fourth) electrode will only fire when the nearest one has eroded enough. To me, it appears that multi electrode plugs is more a marketing move that anything. Maybe some extra duration could be obtained, but not more power or economy, as is frequently advertized. With the recent, MONKEY designed engine compartments in most cars, a looooong plug life can be advantageous (unless you own a well equipped repair shop and well trained mechanics to save your own knuckles!) but otherwise...
In order to properly demonstrate that a given plug design is really better (and makes a difference), requires testing on stationary engines, fully instrumented to monitor plug performance effects. I did quite a lot of testing back in the 80's-90's because we were "designing" new reformulated gasolines intended to reduce air pollution levels in the very high altitude of Mexico City, which is one of the most difficult cities in the world because of 7,350+ altitudes plus being in a valley encircled by high mountains, plus a high solar insolation and warm temperatures. All of these factors aggravate th emissions problem, producing very high ozone levels and chemical smog. I performed complete tests on several types and makes of automotive engines installed stationary and modified to add many sensors and controls to be able to deliver meaningful, repeatable data. At that time we also tested all of the so called "Tune-Up" parameters, like spark plug brand, type, heat range and calibration, ignition system types etc. in order to find the effects not only on emissions, but also driveability, startability and other aspects. One curious, but confirmed finding was related to Bosch brand plugs: the ones with copper cored center electrode, touted for having a great heat range, performed relatively poorly. But the few ones that we could get that were labeled "Cr-electrode" were among the best performing, second only to the (then) best ones (Champion-Plus) this was latter traced to the difference caused by country of origin. The Champion-Plus (remember it was years before Champion was bought and handled by the Federal-Mogul conglomerate (I wouldn't use their present product at all!) was chosen as the best ones for the extended gasoline blends testing. At that time it was Beru, Nippondenso and Bosch the only ones selling here the four projecting ground electrodes design. And yes, it performed slightly behind the conventional single electrode in all cases, even with the platinum central electrode.
The NEW plated " special power producing plugs are JUNK ".
The original platinum wire electrodes in the plugs used by aircraft and racecars worked. The engine HEADS WERE DESIGNED FOR THEM!!! The center electrode WAS PURE PLATINUM, NOT PLATED!
With swirl technology designed into the ignition chamber on modern cars, you have to use single or dual side electrodes, anything else impedes the flame front with reductions of engine performance.
One other suspect not mentioned: most engines USED to have copper core ignition wires to the spark plugs. Radio noise suppresion had the manufacturer installing CARBON CORE wires. These carbon core wires are more delicate....and actually REDUCE the power to the spark plug. Then also tend to find the weakest link ( better ground ) to send the energy to.The carbon core develops gaps and burnouts of the insulation...
My XJ12 had an itermittent high RPM miss. Americanizing ALL the ignition parts in the system ( Crane Cams XR700, Accel coil, MSD wires and single electrode plugs ) cured the problem.
To see if you have a similar problem, just open the hood and see the light show around the components....
P.S. The OFFY used the platinum plugs. I've changed a few sets in my time.
I have previously commented about my possitive Experience with the BOSCH +4 platinum plugs. BOSCH had platinum tipped plugs way back in WW II for use in aircraft engines (with magneto ignition).
It was not till about 1980's they made them in sizes for Automotive uses (with single ground electrode.
Then they introduced the +4 and only latter on +2.
When you look at the +4 design you find that the ground electrodes are to the side of the central electrode and thus do NOT "shroud" the spark, which as pointed out actually happens even with single ground electrode that is ABOVE the central electrode (and only the central electrode is platinum or platinum coated).
The early plugs were in $5.00 range (that is in 1985 when I bought a lot of them, and still have at least 4 sets left over, as I though they would need to be changed eventually).
Today at the price of platinum I doubt the central electrode is 100% platinum wire, perhaps it is only "coated".
Or else how could they sell these plugs for just under $2.00 ?
If the same amount of platinum was used as apparently was back in 1980's then each plug just on the platinum cost should retail for $25 to $30.
I knwo some dealers charge $$$ for replacing of OEM plugs at 100,000 or 120,000 miles but most of that cost I believe is the fact that on some V6 engines you have to disasemble better part of the vehicle jsut to get to the "back" plugs of FWD car.
Ah, the weakness of the proud and haughty engineer type. We are, for the most part, the self-confident fixer's of all the 'things' around us - well, at least the physcial things. And sometimes our wandering outside our areas of expertise costs us a few bucks (like your $1,000 spark plug job).
In my case, my downfall (or at least the one of the many over the years) is my mis-diagnosis of Maytag clothes washer problem. Our washer was fairly old (about 15 years old) and I had done a few simple repairs to keep it chugging along. This time the complaint was that the washer would fill up with water but then would not agitate. So I checked out the wiring diagram and decided that the water level pressure switch - the switch is a very sensitive air pressure switch connected, via a tube, to the tube. Increasing water level equals increased air pressure in the tube which, at a certain water level, would activate it. The switch was in series with the motor start so nothing happened if the water level was too low OR the switch failed.
So I ran a small load with no clothes - just water. When it got some water in it, I shorted out the switch leads and everything started up and ran. Fine - says I - must be a bad switch. Ordered one ($75 ka-ching) and when it arrived installed it.
Ran a test load with a low water level, everything worked great. Ran it again with a test load with a full water level, motor came on and ..... grunt. No agitator action. And the thermal breaker clicked off.
Turns out the problem was a failing bearing in the agitator - Not completely failed - just dragging enough that the agitator would work with a low water level (and no clothes) but would NOT work with more water OR with clothes. A quick conversation with a repair person - way too expensive. Our solution - buy a new washer.
Anyone need a water level switch? I've got two of them.
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