The NGK Iridium Spark Plug, Mercury part number 8M0009927, is the factory-specified spark plug used in many Mercury Optimax and direct fuel injection (DFI) outboards, including the high-performance 300XS platform. This plug is engineered to deliver consistent ignition performance, strong spark energy, and long service life in modern high-output two-stroke engines.
 
In direct fuel injection engines like the Mercury 300XS Optimax, proper ignition is critical for efficient combustion and reliable operation. The NGK Iridium design used in spark plug 8M0009927 provides superior spark stability under the demanding conditions these engines operate in, including high RPM, leaner fuel mixtures, and elevated combustion chamber pressures.
 
Buckshot Racing #77 supplies genuine NGK Iridium spark plugs equivalent to Mercury OEM part number 8M0009927, ensuring the correct ignition component for maintaining performance and reliability in Optimax outboards.
 
Designed for Mercury Optimax and DFI Engines
The Mercury 8M0009927 spark plug is commonly used in Mercury Optimax direct fuel injection outboards, particularly the 300XS Optimax, one of Mercury Racing’s most respected high-performance production engines.
 
These engines rely on precise ignition timing and consistent spark energy to support the air-assisted direct injection system used in Optimax technology. The Iridium center electrode used in this NGK plug helps maintain a sharp spark edge over extended run time, which is important for maintaining efficient combustion and throttle response.
 
Typical applications include Mercury Optimax 300XS 3.2-liter outboards, along with other Mercury DFI platforms that specify Mercury spark plug 8M0009927 in service documentation.
 
Advantages of NGK Iridium Spark Plug Technology
The iridium center electrode used in the NGK spark plug specified by Mercury 8M0009927 offers several technical advantages over traditional copper or nickel plugs.
 
Iridium is an extremely hard and heat-resistant material that allows for a very fine electrode tip while maintaining durability. This design reduces required ignition voltage and promotes a stronger, more consistent spark kernel. The result is improved ignition reliability, especially during cold starts, rapid throttle changes, and sustained high-RPM operation.
 
For Mercury Optimax engines like the 300XS, this consistent spark helps maintain smooth combustion cycles and reduces the likelihood of misfire or incomplete combustion under heavy load.
 
In addition to improved ignition performance, the durable iridium electrode design also provides a longer service life compared to conventional spark plugs, helping maintain consistent engine performance between maintenance intervals.
 
Importance of Correct Spark Plugs in Optimax Engines
Direct fuel injection engines such as the Mercury Optimax 300XS are particularly sensitive to spark plug selection. Using the correct plug specification ensures proper ignition timing, combustion stability, and ECU calibration compatibility.
 
The Mercury 8M0009927 NGK Iridium spark plug is designed specifically to work with the combustion characteristics of Optimax engines. Installing the correct plug helps maintain proper fuel burn, protects engine components from detonation or misfire conditions, and supports the performance levels expected from Mercury’s high-output DFI outboards.
 
During routine maintenance or tune-ups, replacing spark plugs with the correct Mercury 8M0009927 specification helps keep the engine operating at peak efficiency.
 
Supporting High-Performance Mercury Outboards
The Mercury Optimax 300XS remains a popular engine in high-performance bass boats, offshore fishing rigs, and performance lake boats due to its combination of power, efficiency, and durability. Maintaining the ignition system with the proper NGK Iridium spark plugs specified under Mercury part number 8M0009927 helps ensure reliable starting, smooth running, and consistent top-end performance.
 
At Buckshot Racing #77, we support the maintenance and longevity of high-performance Mercury outboards by offering proven service parts used across the Optimax and DFI engine platforms. Using the correct ignition components is one of the simplest and most important steps in keeping these engines performing at their best.
 
Contact mike@buckshotracing77.com or +1-714-697-1716 with any questions.