iridium spark plugs on stock bike

[sickbikers]

Needed clarification,
read a couple of threads about iridium plugs, and could not get a clear answer, not sure if the question was asked, anyway.

Can I use bpreix iridium plugs on a stock 82?

thanks

 

[pamcopete]

SickBikers,

Yes.

 

[Classic]

Doesn't have to be a resistor plug, though. Bp7eix will work.

 

[pamcopete]

Well, you should have some resistance, either in the caps or plugs.

In a dual output, wasted spark system like we have on the later XS650 models, the coil produces a positive voltage on one plug wire and a negative on the other. The Iridium plug is really only beneficial on the negative wire because the idea of the hot center electrode is to encourage the electrons to jump to the grounded electrode. The electrons flow from negative to positive, so the hot tip doesn't really do the job on the positive wire plug.

You can actually check for the negative wire using an ordinary pencil, like this:

Once you have determined which is the negative wire, just install the Iridium on that wire. Install an ordinary plug on the other, positive wire and save the cost of a second Iridium.

 

[sickbikers]

Thanks
So should I use resistor plugs then? on both or just one non resistor plug? if I use one plug, how does that effect the other?

thanks.

 

[sickbikers]

or better yet, what would the benefit of one plug be?

 

[sickbikers]

Im sorry, but to clarify, If i use 2 resistor plugs, on a stock bike, both will work?

 

[pamcopete]

SickBiker,

There should be some resistance in the spark plug circuit. In a wasted spark system, the spark plugs are in series, so you could use one resistor plug (the Iridium) and one non resistor.

As far as the plugs working the same, even when they are matched, they do not work the same because the spark plug with the positive wire needs 40% more voltage to work properly. That's one of the main reasons that a dual output coil in a wasted spark system is a "High Performance" coil. It's really not for High Performance. It's just that the positive plug needs a higher voltage.

Ford motor company recognizes this phenomena by provided one spark plug in each pair with the Platinum on the tip and the other spark plug with Platinum on the ground electrode to equalize their performance, but it still does not compensate for the fact that the hot tip on the positive plug is really not beneficial. It's all part of the price we pay for the wasted spark system, which is simpler and cheaper than a coil per plug, which the auto industry is now going to wards with their coil on plug systems to eliminate the wasted spark penalty.

 

[Tomterrific]

Iridium is long lasting, that's why the center iridium electrode can be so small. The small electrode doesn't quench the spark and allows a greater flame kernal to develop at the point of ignition. These two give more power and more consistant burn in the combustion chamber. Thus the performance benefit is still in both cylinders.

The small electrode is also easier for a spark to eminate from but here Pete mentions that on a dual outlet coil wasted spark system, only one plug sees this benefit. Not so on a points system with teh proper coil polarity.

Don't over think this as the car industry places the platinum for long plug life, 100,000 miles. You can always swap leads every thousand miles like rotating tires to get even wear.

Interesting, ND has an even smaller center electrode than NGK. They make no claims about their plugs lasting longer than standard because of the super thin electrode but performance should be enhanced further.

Tom Graham