What’s New in Spark Plug Technology?
Glancing at a modern spark plug, you’d barely see any differences between it and one from years past, but a closer look under the cladding reveals spark plugs have gotten a lot more efficient…and more expensive.
Standard plugs are designed for a much shorter life when installation is in cast-iron heads, and that cycle doesn’t require newer electrodes with gold, platinum or iridium because you replace them before they exceed this replacement interval.
Fast forward to today, and plugs are designed to last 100K miles and require these advancements in order to meet the newer longer-life specifications.
This expense is due to a number of advancements that spark plug manufacturers have incorporated into their products, things like:
Iridium - Iridium is the new “miracle metal” that is the main reason for the higher cost of premium spark plugs and is also in demand for usage in cell phones and sunglasses. What advantages does Iridium offer?
Iridium is up to six times harder than platinum, and has a much higher melting point which makes the plug last much longer. Iridium allows for a much smaller surface area electrode, resulting in a more concentrated spark pulse and requires a lower voltage to reach ignition point. Iridium is highly resistant to corrosion and demonstrates a lowered arc erosion specification.
These all seem like great things, and they are, but they come at a cost.
Example: A “standard” Honda XR250R spark plug cost is $2.50 and the “iridium” version costs $10.99, so that’s a huge price differential.
Expanded electrode surfaces - This is a fancy name for the new field of funky electrodes you see on plugs such as the Bosch “+4, +4 and IR Fusion” and the E3 “DiamondFire” plug types.
E3 claims the development of a diamond shaped design with a center electrode tip that exposes multiple edges to an engine's combustion space creates higher efficiency. And because electrical impulses naturally follow the path of least resistance, the E3 electrode provides a well-formed spark. When tested, this configuration resulted in a better burn of the compressed air-fuel mixture before the beginning of the exhaust cycle.
Bosch claims the Platinum+4's firing technology combines surface air gap technology, four “yttrium-enhanced” ground electrodes, and a heat-fused center electrode with the most platinum, creating “the most powerful spark you can buy.”
It makes sense that expanded electrode areas would provide additional areas to arc to, creating a more efficient ignition phase.
Capacitive element technology - This is a secondary advancement in spark plug technology and has been pioneered by vendors such as Pulstar.
This is simply a capacitor-type element that is contained in the body of the spark plug, and this element stores input ramp voltages until it reaches peak power, releasing the voltage to the electrode at point of best ignition. Pulstar claims that this technique increases peak power and current during the resistive phase of the spark, as well as increasing electrical to plasma transfer efficiency to over 50% from less than 1%.
Pulstar also has with inconel centerwire electrodes, which perform at higher levels than fine wire iridium electrodes, which also outperform conventional inconel electrodes found in conventional spark plugs.
In talking with Pulstar’s President and Founder, Louis Camilli, we asked: “What factors make the Pulstar plug more (or less) attractive to motorcycle owners?
And his reply was:
Capacitive plugs are at the high end of the manufacturer’s offerings today, but have shown some promising results in both standard and higher performance vehicles.
We used some of the Pulstar plugs as part of this article in our 2008 YZ125 and so far so good. We were going to take photos but the plug still looks brand new!
So if you replace your plugs often, do you need these more expensive alternatives?
We believe the answer in most cases is need…no, but do you want these attributes…yes!
Why? Because many ThumperTalk members own recreational use motorcycles that see short-duration, extreme heat/duty cycles in competition events like motocross, enduro and enthusiastic track days, and this places added stresses on the electrode and surrounding materials, breaking them down and in turn losing efficiency in the process.
Another advantage for these newer plugs is special nickel plating to avoid seizing to aluminum heads, so it can be money well spent.
How to select the right plug for your bike
Most motorcycles have a spark plug specification in their user’s manual, so why would you need to “select the right plug”?
While we agree that the factory recommendation is the best starting point for selecting spark plug type, readers are highly encouraged to learn how to “read the plug” to accurately provide the best model for their particular application.
Here is a reference guide to reading and selecting the right plug based on your usage:
Start with the factory-recommended plug for your bike, and install as instructed here. Ensure you have the proper plug and check the spark gap to factory specification. If out of specification, re-gap it. When gapping spark plugs, the most accurate way is to use a set of gapping pliers. To open the gap, gently pull the ground electrode back. Do not force a feeler gauge between the electrodes and pry them apart. If you want to close the gap, gently tap the spark plug on a solid surface to bend the ground electrode. A little conductive anti-seize is recommended prior to installing in a cool engine. Make sure the spark plug holes are free of any contamination and install with fingers first to guard against cross threading. Screw in until finger tight and torque to factory spec for aluminum or cast iron heads. Note: The crush ring (washer) provides a gas tight seal between the plug and cylinder head through the cold-hot-cold operation of the enginext
Reading Your Plugs
Now, after running your machine in a variety of RPM’s and load scenarios, extract the plug and compare against this chart below.
Keep in mind a light tan or gray color indicates your plug is performing correctly. Darker coloring, such can indicate a rich condition, a cold range plug or too large of a gap.
Continue to follow these instructions until you get your plug(s) to show the best coloration that you can achieve, using this chart as your basic guide (in the Green/OK sections).
Chart photo: NGK
Appears Oil Fouled – Possible Adjustments
Try hotter range plug (longer insulator)
Change fuel ratio for less oil and more fuel in mixture (2 strokes)
Inspect and test for valve seals/worn rings (4 strokes)
Appears Cold or Rich - Adjustments
Try hotter range plug (longer insulator)
Adjust fuel/air mixture (more air needed)
Appears Hot or Lean - Adjustments
Try colder range plug (shorter insulator)
Adjust fuel/air mixture (less air needed)
Maintaining your plugs is fairly simple. When attempting to manually clean the plug you must be extra careful, paying special attention not to change the preset gap. If you do clean the plug you must re-check that the gap is within specification.
There are purpose-built spark plug cleaners that operate off of compressed air with a small bag of silica that’s used as the cleaning material and we recommend these units over manually trying to clean the plug with solvents and wire brushes.
If you want to clean a spark plug, here’s how NGK recommends doing it:
If the firing end is wet, make sure you clean the spark plug with
a quick drying cleaner. (Examples: contact cleaner or brake cleaner). Sand blast the spark plug using low air pressure and use a dry compound. Completely blow all the sand from the spark plug. Using a wire brush clean the threads and re-gap.
The Bottom Line
Today’s new iridium based spark plugs can provide a hotter spark and a cleaner burn under many different load conditions, and can remain cleaner for longer durations than the conventional copper plug.
The new capacitive element plugs like the Pulstar have shown to provide additional benefits over the iridium plugs including moderate fuel savings and lowered hydrocarbon emissions.
The bottom line is for longer life, cleaner burns and less maintenance, using the newer types of spark plugs as described here are worth every penny.
Bosch Enerpulse/Pulstar E3 NGK