M157 HKS Spark Plug set (5.5 Biturbo)

HKS Spark Plugs to suit M157 5.5 litre BiTurbo engines.

(set of 8)

A noticeable difference in performance over other brands. 

• Iridium Alloy Center Electrode
  Iridium alloy center electrode reduces voltage requirement and improves ignition performance and durability.
• Outer Electrode with Platinum Chip
  The outer electrode incorporates a square platinum chip which improves durability, and combining with the iridium center electrode boosts ignition performance.
  The outer electrode features a shortened tip design and tapered shape while maintaining the necessary space for proper ignition.
• Short Type Outer Electrode (Anti-Vibration)
  The outer electrode has been shortened and engineered with the ideal shape to decrease weight for resistance against vibration. This anti-vibration design improves longevity of the outer electrode.
• Thermal Edge
  After long idling or under various combustion conditions, carbon buildup can occur causing misfires. The thermal edge of the ceramic insulator discharges to help decrease carbon deposits.
• Spark Support Gap
  Discharge occurs in the spark support gap (space between the tip of insulator and the base of the outer electrode) to help prevent carbon buildup.

Choose from standard heat range (Suggested for up to stage 2 vehicles) or colder heat ranges 

About Spark Plug Heat Range:

Hot Plugs    

Have a longer insulator that prevents heat transfer into the water jackets. It keeps more heat in the tip of the spark plug, which helps burn off combustion chamber deposits. But if there's too much retained heat, the engine will experience preignition.

Colder Plugs    

Gave a shorter insulator and retains less heat at the tip end are only required when higher boost levels cause increased cylinder head temperatures. If the plug is too "hot" pre ignition may occur. —but if it's too cold, deposits accumulate and eventually the plug will foul.

Understanding HKS Heat Ranges

HKS spark plugs for the Mercedes M157 engine are available in multiple heat ranges designed to match your power level and driving conditions.

• Standard Heat Range
  • Best for stock to Stage 2 vehicles
  • Ideal for daily driving and consistent cold starts
  • Provides optimal self-cleaning and long service life
• 1-Step Colder
  • Designed for higher boost and increased cylinder pressure
  • Recommended for Stage 2+ and Stage 3 builds
  • Helps prevent spark blowout and pre-ignition under load
  • Common upgrade once exceeding ~60–100 hp over stock
• 2-Step Colder (Extreme Use)
  • Intended for high horsepower builds (800+ hp)
  • Required for hybrid turbo setups and ethanol fueling
  • Maximizes heat dissipation under extreme combustion conditions

A colder plug is NOT “better” by default:

• Too hot → knock, detonation, overheating
• Too cold → fouling, rough idle, misfires

The goal is correct heat range for your setup, not the coldest option.

Spark Plug Gap Guidance

(All high-performance plugs require proper gapping)

• Stock / mild tune: ~0.028–0.032"
• High boost setups: ~0.022–0.026"

Proper gap is critical—these plugs are designed for high boost but must be set correctly during installation