racing plug
 

Building a 3.6 air cooled track motor. Looking at NGK and I have choices between Iridium or standard non resister plug. Advantage one way or the other? Thanks, Bob

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I'm going with NGK B9EG for the 14mm plugs and D9EA for the 12mm second plugs. [edited to correct diameters]

Turns out I asked the same question a couple years back. Here's what people said then.
http://forums.pelicanparts.com/911-engine-rebuilding-forum/1069484-sparkplugs-race-motor.html

I am running Brisk BR12S silver plugs in my race engine and love them. They are better than the NGK iridium plugs I had been using….silver is a MUCH better conductor than iridium…

The conductivity difference in silver, copper, platinum, iridium, etc. of the plug electrodes makes no difference in performance for several reasons. First, compared to the resistance of the spark gap, they are orders of magnitude lower resistance. Second, compared to the resistance in either resistor spark plugs or resistor wires, the resistance of the metals in the electrodes is miniscule. Third, very little current jumps the gap to make the spark. In P=IV, the V is very large (20,000-40,000), and consequently, the I is very small. Thus, the difference in spark energy is insignificant.

I'm only talking about the metals in spark plug electrodes here. Different spark plugs do work better or worse in different engines, based on their electrode shapes, orientation, heat characteristics, etc., but the conductivity of the metals is not one of them. The reason to use exotic materials is to make the plugs more resistant to electrode erosion, thus lasting longer.

How much does you track engine differ from stock?

Plain copper single electrode NGK plugs works very good and are inexpensive.

If this is a NA engine, you have a lot more choices. A non resistor plug will give a little more energy at the firing end but could induce some electrical inference to sensitive electronics. Most race plugs are non resistor.

Can you use a street plug in a racing engine. Of course, you can. The only person to stop you is yourself. If it survives, and the plug appears to “work”, go for it.

In most club racing 911 NA engines where a street plug is used, the engine probably does not make enough cylinder pressure to affect the street plug. In many cases the Ignition type limits the cylinder pressure developed and saves the street plug from destroying itself.

The simplest differences between the two plugs is construction and heat range. The construction has more effect on the plugs heat range. Race plugs typically use a thicker center electrode made from material that will withstand the abuse a race engine demands of the plug. Detonation, cylinder temp and pressures all work against a finer precious metal wire plug. Although it takes more energy to fire a thicker electrode. Most race engines have Ignition systems that can do this, more so that street engines.

Race plugs will typically have a shorter electrode, or less of it outside of the plug chassis. Shorter ceramic insulator as well. Often this is to shield the plug from the in-cylinder stress and in some cases also to give piston clearance.

Today, race plugs have taken on a whole new construction at both ends of the plug. Smaller chassis sizes are common now, 10.00mm and 12.00mm are standard sizes now. Finding 14.00mm plugs today is getting harder and harder.

We are using 10.00mm plugs exclusively now as there are more choices for different applications. I am seeing a convergence between plug construction for normally aspirated and turbo engines. What we use for either is more about the electrode position in the chamber. Now we are seeing extended firing ends into the chambers for Turbo engines. The DI engines have driven this technology with swirl “pots” built into the piston crowns trapping a small amount of mixture that the plug ignites. This technology is more about pressure and temperature-initiated ignition than spark ignition. It has opened the ability to produce more torque with leaner mixtures.

Looking at a 14.00mm race plug from any manufacturer you choose to use, it will have the appearance of an older style plug. However, it will last longer, give less trouble and will be easier to read the Ignition advance and fueling.

If you use a street plug with a fine wire, it can be read the same but typically the race plug will be cooler and will not show any boiling happening. Sadly, in many cases the plugs are never “read” and unfortunately some do not know how to.

This is incorrect. Especially in race engines where cylinder pressures and temperatures can be much higher. You want to use iridium plugs in a race engine? Go for it. My high compression race engine runs better with Brisk silver race spark plugs. Again the superior electrical and thermal conductivity of silvers certainly comes into play here.

Scott, I know you have a lot of experience racing, so by all means, run the plug that works best in your engine, especially for a race engine. I'm just saying that the electrical conductivity of the materials is insignificant in the total picture of what makes a plug good for your application. Thermal conductivity depends more on the design of the plug--how long the electrodes are, how short the insulator is, the shape of the electrodes, how far they protrude into the combustion chamber, the heat range of the plug, etc., than the inherent characteristics of copper or nickel or silver or whatever. I'll bet that the Brisk Silver plugs have very little silver in the electrodes. Silver would erode away very quickly due to heat, so it must be some alloy with lower thermal conductivity than pure silver.

Whatever works best for you, go for it. Just don't go shopping for plugs based on marketing claims about the materials they are made of. How those materials are combined into the overall design is far more important. And that applies to race plugs or street plugs.

"""Whatever works best for you, go for it. Just don't go shopping for plugs based on marketing claims about the materials they are made of. How those materials are combined into the overall design is far more important. And that applies to race plugs or street plugs."""

Could not have said that better myself!!!! Well said by someone who understands and knows.

Its unfortunate and common, that the mistake you advise not do believe in, is all too often fallen for.

Today, the reliance on sensors to tell us the fueling and the Ignition angle is typical. It works really well and I use it too. Until it doesn't work and then what? I have had many customers who had the bad experience of burnt pistons from bad fuel, the wrong fuel or the wrong mapping. If only they had inspected the spark plugs it may have saved their engines. Unfortunately, all of them did not know how to read a plug. They do now.

It matters! Regardless of how much the rest of the system is impacted by resistance, the spark still has to make the jump across the electrodes. Silver makes that easier than iridium.

The electrical conductivity becomes quite important in situations where you have high cylinder pressures. That is where you want the most electrical conductivity possible. How hard it is for that spark to generate between the center electrode and ground electrode is most certainly affected by the electrode material choice. The better the electrical conductivity, the better the spark plug handles higher cylinder pressures.

A little clarity in simple terms. Imformation from PRI tech reports.

Was just going to post something similar.

Sparkplug manufacturers select materials for their products based a few different factors. Thermal and electrical conductivity are two of them. For performance/racing engines in which we we may be willing to replace sparkplugs more frequently, these are important. There's also corrosion resistance for a long lasting sparkplug.
Copper conducts electricity well, but doesn't resist corrosion that well, and it melts at a low temperature.
Nickel and platinum do all three decently.
Iridium does OK too, but is very resistant to corrosion. Makes a great 100,000 mile plug. Not necessarily the best for performance though.
Silver does all three well. It's expensive, probably why only premium sparkplugs use it.

Has anyone done back to back dyno runs with different plugs to determine actual performance advantage?

When I worked at Garretson’s with Jerry Woods he said run silver plugs. So in my S I run W4CS and in my race engine XR2CS. The silvers were 1/2 the cost of platinums and I have a lifetime supply. In projects I had picked NGK Iridium but will probably switch to copper if needed, like in all my old service days, where I never had any problems with them.

Many years ago in my Formula One days, John Glover (sadly missed) who was the Champion engineer at all F1 races, told me they choose Silver for its thermal conductivity to remove the temperature away from the electrode not for any electrical conductivity.

It may have had some electrical benefits, but it was the thermal characteristics that Champion in those days were looking for.