Projected spark plug electrode, purpose and effect?

Fast Eddie · May 5, 2017

Gents,

I have been running NGK BR8EIX plugs in my Commando. I also bought, and tried, NGK BPR8EIX. The P stands for 'Projecting'' and refers to the fact that the centre electrode and its insulator project 1.5mm ish into the combustion chamber.

The theory is that being located more centrally in the combustion chamber helps the burn and helps the plug stay cleaner.

I'm struggling to understand how a mere 1.5mm could make any discernible difference! And my back to back runs don't show any difference at all.

So, are there any real pros / cons?

SteveBorland · May 5, 2017

My bevel Ducati really likes the projected tip plugs - they do not foul as easily as std plugs in traffic. The ididium tip on your plug does much the same thing though.
The projected tip allows the plug to have a much wider heat range seemingly.

/Steve, trying to get the 850 back together again. Nearly there

pommie john · May 5, 2017

Are you sure it's only 1.5mm? I have some downstairs and from memory it's nearer 5mm

Danno · May 5, 2017

1.5mm doesn't sound like a lot, but when you figure the speed of combustion, it's a pretty good difference. Projector plugs are less likely to foul because the center electrode isn't masked by the outer threaded case and can more easily rid itself of combustion byproducts.

SteveA · May 5, 2017

Fast Eddie said:
Gents,

I have been running NGK BR8EIX plugs in my Commando. I also bought, and tried, NGK BPR8EIX. The P stands for 'Projecting'' and refers to the fact that the centre electrode and its insulator project 1.5mm ish into the combustion chamber.

The theory is that being located more centrally in the combustion chamber helps the burn and helps the plug stay cleaner.

I'm struggling to understand how a mere 1.5mm could make any discernible difference! And my back to back runs don't show any difference at all.

So, are there any real pros / cons?

I am running the Denso IW27 on a race bike, equivalent to NGK...9EIX, they didn't foul yet! and at one stage colder I would have thought they would be more likely to than the 8EIX!

I am not surprised you can't tell the difference. If there is a (possibly anal) way to improve things surely it is using spacers to ensure that the outer electrode is held a way from the centre of burn! Doing this I would prefer the projected plug only to ensure that the spark remains fully in the chamber and not in the thread hole, but I doubt you would need spacers that thick that they would affect that.

kommando · May 5, 2017

I have been using projected plugs for 30 odd years, used them on a B40 to get easier cold starts which seemed to work so carried it over to every bike since then, not looked for any other advantages but it did seem to reduce the number of kicks needed on cold mornings.

NKN · May 5, 2017

Tried some on a 450 CL last Sunday. Have to be real carefull because after 50 miles I took them off to see that the negative electrode was being slightly touched by the piston. Or was it a valve? Didn't heard anything but it was in contact.

Projected spark plug electrode, purpose and effect?

Hard to see in the picture but if you look close enough to the right one, you'll see a flat on the negative electrode.

Otherwise not felt any difference.

There is something that French rallymen (and others too I believe) were doing, it was to cut a little of the negative electrode to have the spark without any "wall" in front of it. Was good for the torque they used to say.

acotrel · May 6, 2017

The porcelain insulation conducts heat. If the plug's heat range and the carb jetting and ignition timing are correct, most of the porcelain will be white and there will be a 1mm black ring on the porcelain right down inside the plug where it meets the metal. The plugs in the photos seem to indicate that the motor might not be operating at it's optimum - probably needs a new throttle cable ?

nickguzzi · May 7, 2017

Porcelain is not a very good thermal conductor.
The porcelain insulator has a formed ring which abuts up against the plug body inside with a fire ring. The length of the insulator nose beyond the seat is the big determinant on the plug's heat range.

Projected tip plugs, because they start the flame front nearer the far wall of the combustion chamber, will need less advance.
Older engines, designed before projected tips were around or at least commonly used, will need adjustments to their ignition timing to avoid timing related problems.
I think 2-3 degrees was the old rule of thumb. That may have been to one specific engine design though.
It is not impossible that each engine will need empirical testing to optimise timing after a change, one way or the other, due to the differences in combustion chamber shape and sparkplug position, and all the swirl, tumble and\or masking effects.

Fast Eddie · May 7, 2017

pommie john said:
Are you sure it's only 1.5mm? I have some downstairs and from memory it's nearer 5mm

Measuring to the top if the porcelain, the stock plug is slightly recessed by approx .5mm. The projector plug projects by 1.5mm, so the difference between stock and projector types, with this plug, is 2mm.

gripper · May 7, 2017

As Steve A says, some people index their plugs to ensure the side electrode doesn't mask the spark from the centre of the cylinder. Strikes me that they need to get a bit more :lol:

acotrel · May 7, 2017

Normally the ignition advance is adjusted to suit the fuel and the motor's compression ratio (and in some cases the revs). The compensation is achieved by changing the carb. jetting. Changing the type of plug has minimal effect, and adjusting the jetting should be enough to cope with it. The difference in heat ranges of various plugs means that you end up changing the main jets if you do plug chops. In the end, if the black ring down inside on the porcelain disappears, you are in the danger zone. If you are tuning a bike, it might be smart to use a hotter plug until you get the jetting right, then fit the cold ones. It means the black ring on the porcelain will disappear quicker as you lean off when you are doing plug chops and changing main jets. My motor always runs rich on the mains while the midrange is as lean as possible without creating a miss. For a road bike, you might need to run slightly richer in the midrange, but lifting the needles one notch is a really big step.

gortnipper · May 7, 2017

A projected plug firing tip temperature is increased by 10°C to 20°C

comnoz said:
What make a plug consider to be a hot plug is the fact that the electrode has a long path to the cool metal around it. Water cooled engines generally run a "hot" plug because the head is cool and draws the heat from the plug. Air cooled motors generally need a cooler plug because the head is hotter. If you run a plug that is too "hot" then there is the possibility of the electrode reaching a high enough temperature under hard use that it begins to glow. At that point it will ignite the fuel air charge before the spark happens causing dramatic and serious engine damage such as holed or siezed pistons.

Norton motors generally use a NGK heat range 7 for normal use or 8 for hard use. Autolights #64 plug equates to a heat range 5 in NGK.
There are other factors that go into determining whether the plug will reach dangerous temperatures such as plug projection but I would think a plug of that heat range would be in the danger zone under heavy load. I have not tried app64 plugs.

You can make a plug run cool by running a rich mixture but that will take away a lot of power and fuel economy.

Any Norton motor I have tuned for maximum performance needed a NGK #9 or #10 plug to keep the electrode cool enough. Jim

This is an interesting thread spark-plugs-t8008.html

With your motor, which one is working better? I was planning on running a BPR8ES or similar in my new motor.

Fast Eddie · May 7, 2017

I run number 8 normally, 9 for track days just for safety. Can't tell any difference between the 2. Nor can I tell any difference between normal and 'projector'.
I only use iridium plugs.

Danno · May 7, 2017

The only difference is a bit more resistance to fouling with the projectors.

gortnipper · May 8, 2017

http://www.ngksparkplugs.ca/tech-info-spark-plugs.cfm

Projected spark plug electrode, purpose and effect?

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