Electrode Less Plugs?

Don't expect to get huge amounts of power from them. The power is produced from energy in the fuel and if you light the fuel air mix with a fancy spark plug or a match it will still release the energy.

 

NGK copper plugs have always been reliable for me.

 

The plugs are surface discharge and I have used them in my 748R on the road and track. They are really meant as a race plug only and I found they fouled easily when using them on the road and starting is often harder.

One time when you do need them is if you have a high compression motor as otherwise if you don't the pistons hit the plug electrode on a stock plug.

My son has a race 748 motor built by CJS and he can only use this type of plug.

They are very expensive on eBay but they can be had quite cheaply from certain internet plug sellers, I think I paid about £6 each for mine at the time.

 

Okay, but my next question would be; in what way have the standard plugs caused reliability problems?
I was not trying to be sarcastic, but as an engineer I like to to see the reasons that things are changed and the problems that are solved by changing those things.
I took the plugs out of my newly acquired ST2 yesterday to find that it had the NGK Iridium plugs fitted. They have the thin centre electrode. I can see the advantage of this type of plug on a very old engine with a magneto ignition system where the spark could be weak when starting, but on a modern electronic system? I would suggest that for the same price of one of those plugs you could buy three normal plugs that would last much longer.

 

This has been mentioned on here before and a search will reveal several comments on which is better along with certain theories as to which is better to use. One is that iridium plugs allow you to run a larger spark plug gap which allows a fatter spark and more efficient burning.

 

But the theory suggests that a given amount of energy (25,000 volts) will jump a certain size of gap. If one electrode is smaller or made from a different metal then how would that gap be better jumped? If your spark is 0.8mm or 1mm does it ignite a very explosive mix of fuel differently?

 

Once the surface discharge plugs start to foul up they lose quite a bit of power in the spark, the "gap" such as it is will remain the same. They are quite a cold plug which doesn't help, and from experience they foul up quite quickly and even cleaning doesn't improve them that much.

They were a Ducati recommendation for certain 748's like the R and SPS but in practice they just don't work that well. I noticed a big improvement when I removed mine and replaced them with stock type plugs.

 

theory behind them was that they give a stronger fatter spark, , and assisting the flame front making them ideal for very high states of tune. As Red has said though they (the Ducati ones at least) are designed within an operational performance range, and in road conditions they'll just die prematurely.

On a road bike its a bit of a waste of money as you'll not see the full benefit of them.

That's not to say that there aren't surface discharge plugs that are the same rating as your existing road plug, its just hunting them down. maybe the Japanese manufacturers have something on one of their models?

 

"theory behind them was that they give a stronger fatter spark"
They must have some sort of amplifier built into them then.
Even if they were able to make a stronger fatter spark, would that make the fuel air mixture explosion have more energy than the fuel contains?

 

the electrode is fatter, and the surface area is greater.

standard plug: ground electrode sticking down and gap fed by the resistance coil. - spark arcs between gap and electrode.

surface discharge: ground electrode is the outer ring so the spark discharges across its whole circumference surface.




vs



you improve it by adding more electrodes:


but like valves, it comes down to surface area. the more surface you have to spark the greater the chance of even ignition burn and the prospect of limiting misfire.

 

But as I said even the smallest spark will light the explosive mixture in the cylinder and even if you have ten big sparks it will still only light the mixture.

 

but if one spark fails then that's it. whereas the chances of failure of all ten sparks are reduced. In racing as in any harsh environment, performance is measured not just in HP gains but also in rate of failures. last thing you want when leading the pack at the top level is to start misfiring and forced to retire. Sometimes you need the lowest common denominator to be reliable.

lets use an analogy;
I can burn a sheet of paper by striking a match and holding it under the centre just as easily as I can by firing up the big ring on my hob and putting the paper on it. The result is the same.
However the match has a greater probability that it might blow out before igniting the paper, the likely hood of the hob ring less so.
The hob ring also has a greater chance of burning the paper in its entirety rather than leaving a chunk unburnt.

So you're absolutely right Bob, the effect is the same. All you're doing is trying to ensure that the effect is as optimal and reliable within the operational range of your application (racing) as it can be.

 

I have to use the surface discharge plugs, and have had them foul up just trying to start it. It's fine when warm, but from cold was a pain.

 

that's probably more down to the fact that the rating isn't correct. The racing ones will be a very cold plug, not a problem when you've pre-heated the engine anyway. This is what I was saying, if we can find a plug of the right rating for your engine, then there really shouldn't be a problem.

As Mr R says Dyno time costs money but its money well spent. I've never regretted the money I've thrown at rolling road as I can genuinely say I've felt the benefit the minute I've ridden out of there.

Nice engine spec by the way Steve I bet the bike is lovely

 

NGK's own words on the matter:

6. Using "Racing" Spark Plugs

Be cautious! In reality, most "racing" spark plugs are just colder heat ranges of the street versions of the spark plug. They don't provide any more voltage to the spark plug tip! Their internal construction is no different (in NGK's case, as all of our spark plugs must conform to the same level of quality controls) than most standard spark plugs.

There are some exceptions, though. Extremely high compression cars or those running exotic fuels will have different spark plug requirements and hence NGK makes spark plugs that are well-suited for these requirements. They are classified as "specialized spark plugs for racing applications". Some are built with precious metal alloy tips for greater durability and the ability to fire in denser or leaner air/fuel mixtures. However, installing the same spark plugs Kenny Bernstein uses in his 300+ mph Top Fuel car (running Nitromethane at a 2:1 air/fuel ratio and over 20:1 dynamic compression) in your basically stock Honda Civic (running 15:1 a/f ratios with roughly 9.5:1 compression) will do nothing for you! In fact, since Kenny's plugs are fully 4 heat ranges colder, they'd foul out in your Honda in just a few minutes.

NGK as a company tries to stay clear of saying that a racing spark plug (or ANY spark plug) will give you large gains in horsepower. While certain spark plugs are better suited to certain applications (and we're happy to counsel you in the right direction) we try to tell people that are looking to "screw in" some cheap horsepower that, in most cases, spark plugs are not the answer.

To be blunt, when experienced tuners build race motors, they select their spark plugs for different reasons: to remove heat more efficiently, provide sufficient spark to completely light all the air/fuel mixture, to survive the added stresses placed upon a high performance engine's spark plugs, and to achieve optimum piston-to-plug clearance.

Some of these "specialized racing plugs" are made with precious metal alloy center/ground electrodes or fine wire tips or retracted-nose insulators. Again, these features do not necessarily mean that the spark plug will allow the engine to make more power, but these features are what allow the spark plug to survive in these tortuous conditions. Most racers know screwing in a new set of spark plugs will not magically "unlock" hidden horsepower.

 

You're absolutely correct.
But as the radiator ideally needs to come off for an easy front plug change it doesn't happen until it fails.
FWIW compression ratio's about 14.5/1 but I can run on super unleaded.

 

This is ringing alarm bells for me. I will be running my 748RS engined track project which runs Champion surface discharge plugs (67040211A) at Cartagena in March for the first time. I have been advised that the plugs have a reputation for fouling if the engine is not warmed up and kept at a "high" tick over of about 2500rpm. The engine has been run in on the dyno using standard unleaded with satisfying results as I asked for reliability not outright power. I have spare plugs but is there anything I need to do or more likely not do ? Loving the technical discussion gents, thanks . Andy