Lars G. Johnsen wrote:
>
> Know that there are other new and improved plug designs out on the
> market: anyone had any experience with those?
When the price of platinum plugs came down a bit from `80s prices, I
bought a set of those and am still running them. As for odd-patterned
ground electrodes, there's not much to commend or abuse them, I suppose.
There was a thread on the diy_efi list recently about Splitfires,
commenting on a US ruling that the Splitfire manufacturer cease and
desist advertising power, mileage and emissions gains, since those were
not proven in practice.
In theory, an arc traveling from the center electrode to the ground
electrode will deposit metal from one to the other, and corona theory
says that electron travel depends considerably on the sharpness of the
emitting electrode, because of the concentration of charge on a sharp
point (have seen this to be true in the lab). More electrodes would seem
to make an arc more likely to happen, but I have the feeling
(unsubstantiated by data) that multiple electrodes probably erode and
thus lose good electrical surface at about the same rate, so the
difference in performance is small. As well, there may be disruptions of
the flame front by multiple electrodes, so having a spark because of
multiple ground electrodes may not translate to far better performance.
However, I will mention one curious case. Every once in a while, when I
worked at a Toyota garage, a Tercel with a 3AC engine would come in on
the hook, dead as a doornail. The owner would invariably say, "I just
had it tuned up a few days ago." Here? "Uh, no," the owner would say. In
every case, there were Champion plugs installed, of the correct heat
range and nose configuration as the stock Nippondenso plug. They simply
refused to start the car, however. When the plugs were removed, they
showed about as much wear and as many deposits as one would expect from
any other plug with that amount of use. None had severe blistering or
melted electrodes or charcoal on the insulator which might indicate the
conversion chart was incorrect. They simply did not work.
In every case, installing new OEM Nippondenso plups solved the problem.
In theory, the only discernable difference in the design of the plugs
was the ground electrode. Champs have what one would describe as a
traditional electrode, while the Nippondenso's had a square groove cut
in the underside of the ground electrode. The theory says arcs start and
travel to sharp edges, and the groove in the electrode provided double
the sharp edges of a standard electrode. The reason for the plugs'
failure may have been something simple, but the answer evaded me. I even
saved the plugs and put them in other engines, just to see if the
problem traveled with the plugs, and it did not. I suspect that it had
something to do with one or more of three things. One, the plugs were a
standard Champ design from the days prior to HEI ignitions, and the
plug's insulation had broken down and tracked to ground (not likely,
since they worked in other cars with HEI ignitions). Two, the groove in
the OEM plug did make a difference, for theoretical reasons, and three,
there was something about the engine's combustion chamber shape which
made the Champion plug ill-suited for the application. Never did
definitively find out.
<g>
Cheers.
--
My other Triumph doesn't run, either....
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