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Guys,
There's a diagram and discussion from Champion over at:
http://www.edelbrock.com/automotive/sparkplugs.html
Here's another discussion:
http://se-r.net/engine/specialty_spark_plugs.html
Bosch also apparently makes surface air gap plugs in their Platinum+4 and Platinum2 lines. I've not seen any of these plugs but they might be worth chasing. Here's Bosch's description of them:
"Q. What are the advantages of surface air gap plugs such as Platinum+4 and Platinum2? A. To validate the improved performance of surface air gap plugs with a pure platinum core and multiple ground electrodes, extensive testing was conducted in the laboratory and in the field:
a.. The first test measured the energy transfer efficiency of the four-electrode platinum plug compared to conventional and other premium plugs with a single ground electrode. This certified laboratory test measured the additional pressure generated by the spark discharge in a pressure chamber. Higher pressure equals a higher energy transfer by the spark. The test showed that the four-electrode platinum plugs transferred more energy to the air/fuel mixture resulting in improved driveablility and lower emissions.
b.. As a spark plug wears via erosion and corrosion, the gap between the center electrode and ground electrode gets larger. The larger the gap, the more voltage is required to produce a spark, until the capability of the ignition system is exceeded and the plug misfires. It was found that the multiple ground electrode, pure platinum center electrode plug reduces gap erosion and increasing voltage requirements over time.
c.. Roush Industries, an independent test lab, measured the fuel consumption for the four-electrode platinum plug, as well as, that for original equipment and other premium single ground electrode plugs. Fuel savings up to 4.8% were found in the four electrodes, platinum core plugs. Tests were conducted in accordance with Federal Test Procedure 75FTP and HFE.
d.. Tests for carbon fouling were simulated in a cold cell by repeatedly cooling, starting and operating the engine without letting the spark plugs reach their self-cleaning temperature. This cycle does not let the spark plug reach its self-cleaning temperature and allows the formation of carbon deposits. The tests found that the four ground electrode spark plugs had up to 33% better cold restart reliability than conventional plugs."
Of course, surface air gap or not, the nose of the plug still can't project into the housing where it can be swept by the apex seal.
Barry Gardner
Wheaton, IL
Anyone know whether these plugs are still available? It would seem that if nothing else, it might make cleaning the lead a bit easier.
Charlie
Actually,Charlie, they still make them and they are available. Jason had them in his engine at Pecan Plantation. I looked into using them but when I read that one of the possible short-comings of this type of "surface gap" plug was fouling, I decided not to even buy a set, but wait until Jason reported back on how his were working out. I agree they would appear easier to clean once they fouled, but if they fouled twice as readily, not much gained {:>)
Ed
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