Ruthenium Spark Plugs: Should you use them on your Ecoboost?

EcoBoost engines, particularly under high boost, place high demands on the ignition system. One spark plug worth evaluating is the NGK Ruthenium HX™, specifically the PSPE-style variant used in many direct injection turbocharged applications. Compared to traditional Iridium plugs, these exhibit distinct combustion behavior that can influence both performance and calibration strategy.

Combustion Pressure and Stability

Below is NGK’s combustion pressure consistency comparison between their Ruthenium HX and a conventional Nickel plug. The Ruthenium plug produces a more uniform pressure trace across combustion cycles, indicating lower cycle-to-cycle variation. An Iridium IX typically performs somewhere between the two.

This matters in boosted engines, where combustion instability can lead to knock, misfire, or unpredictable torque delivery. Greater stability supports tighter control of ignition timing, especially under transient load or wide-open throttle conditions.

Flame Kernel Propagation Characteristics

NGK’s flame kernel growth tests show differences among Ruthenium HX, Iridium, and traditional Nickel plugs:

By ~2 milliseconds post-ignition, the Ruthenium plug exhibits a ~1 ms faster flame front expansion compared to the others. This suggests combustion initiates earlier and spreads more effectively, reducing the time needed to reach peak cylinder pressure.

The result is that less spark advance may be required to reach MBT. This aligns with what I’ve observed in logs: final timing often appears slightly retarded with Ruthenium HX, yet torque output and peak achievable air load remain stable or even improves. The reduced advance isn’t a sign of knock or inefficiency—it reflects faster combustion and a shifted pressure curve.

While these changes are subtle, they remain relevant, particularly when optimizing ignition at high boost or when running ethanol blends, where that flame speed plays a larger role.