For Mercury high-performance 2-stroke outboards, especially modified 2.0L, 2.4L, and 2.5L V6 engines, an iridium spark plug can offer real ignition advantages over a conventional nickel-electrode plug.
Engines such as the Mercury Racing 2.4L Bridgeport EFI, 2.5L 245 Carb, 260 EFI, 280 ROS, 300 Drag and S3000, along with modified 150, 175, 200 and 225 HP Pro Max, Super Magnum, XR and XRi-based performance builds, can operate at very high RPM and cylinder pressure. Under those conditions, reliable spark initiation becomes increasingly important.
The NGK BR8EIX (6747) and BR9EIX (3089) are Iridium IX resistor spark plugs with a fine-wire iridium center electrode. NGK identifies Iridium IX as a performance-oriented design intended to provide high ignitability, stable spark characteristics, anti-fouling performance, and excellent electrode durability.
For Buckshot Racing #77 billet race heads specifically machined for a 3/4" spark-plug reach, the BR8EIX and BR9EIX provide two useful heat-range choices. They use the same basic 14 mm long-reach plug format; the major tuning difference is that the BR8EIX is NGK heat range 8, while the BR9EIX is one step colder at heat range 9.
Why Iridium Makes Sense on a Mercury Racing Two-Stroke
The main advantage of Iridium IX is its fine center electrode. A smaller firing tip requires less voltage to initiate the spark than a larger conventional nickel electrode.
On a properly tuned high-performance Mercury V6, that can help maintain consistent ignition as cylinder pressure rises during hard acceleration and sustained wide-open-throttle operation.
Iridium also has a very high melting point and strong resistance to electrical erosion. NGK specifically cites a stable spark, anti-fouling characteristics, and durability among the advantages of its Iridium IX design.
This does not mean an iridium plug automatically produces more horsepower. Its benefit is primarily ignition consistency, fouling resistance, and electrode durability. Those characteristics become valuable on engines that regularly see 7,000 RPM and beyond, provided the plug heat range, reach, gap, and engine tune are correct.
BR8EIX – Heat Range 8 for Mixed High-Performance Use
The BR8EIX 6747 is the hotter of these two plugs. Because it retains more firing-end temperature than the BR9EIX, it is generally the better starting point for a Mercury performance engine that sees a mixture of idle, cruising, acceleration, and shorter high-RPM runs.
For a compatible 2.0L, 2.4L or 2.5L Mercury V6 fitted with Buckshot Racing #77 3/4" billet heads, BR8EIX is a strong choice for lake racing, recreational high-performance boating and modified Pro Max or carbureted/EFI combinations that are not operated continuously at maximum load.
The warmer heat range also gives it more resistance to low-speed carbon and oil fouling than a colder racing plug when the boat spends meaningful time below wide-open throttle.
BR9EIX – Heat Range 9 for Sustained Racing
The BR9EIX 3089 uses the same basic long-reach Iridium IX architecture but is one heat range colder. NGK heat-range numbering works in the opposite direction many people expect: a higher NGK number represents a colder plug.
That colder characteristic makes the BR9EIX more appropriate when combustion heat is elevated by higher compression, sustained high RPM, aggressive race tuning, or prolonged wide-open-throttle operation.
For dedicated Mercury Racing combinations based on the 2.4L Bridgeport, 245 Carb, 260 EFI, 280 ROS, 300 Drag or S3000, a BR9EIX can be the more appropriate choice when using a compatible 3/4"-reach billet head and the engine is operated primarily under severe racing load.
Brucato's published guidance also uses a colder heat-range-9 resistor plug family for the Mercury 2.4 Bridgeport, 260 and 300 Drag, reinforcing the general principle that these higher-output race applications often call for the colder heat range.
Long Reach 3/4" Reach vs. Standard 1/2" Mercury Plugs
The most important fitment distinction is spark-plug reach. The BR8EIX and BR9EIX are long-reach plugs at approximately 3/4" (19 mm).
Many original Mercury two-stroke cylinder heads use a shorter 1/2" (12.7 mm) reach plug such as the BR8HS or BR9HS family.
Our Billet Race Heads - 3/4" long reach BR8EIX / BR9EIX configuration
That means these Iridium IX plugs should be selected because the cylinder head was designed for that reach—not simply because the engine is a Mercury 2.4L or 2.5L. Installing a 3/4" plug in a head designed for 1/2" reach can project the threaded section and firing end too far into the chamber. A 1/2" plug in a 3/4"-reach head will sit too far back.
Useful NGK Cross-References
For builders familiar with standard NGK plugs, the BR8ES is the conventional nickel-electrode comparison in the same general long-reach, heat-range-8 family, while BR8EIX provides the Iridium IX fine-wire alternative.
Likewise, the BR9EIX provides the corresponding colder heat-range-9 Iridium IX option in the long-reach format.
Do not confuse these with BR8HS or BR9HS. The HS-series uses the shorter 1/2" reach and is physically intended for a different cylinder-head thread depth.
The long-reach EIX plugs become relevant when the cylinder head itself is designed for the 3/4" reach, such as the Buckshot Racing #77 billet race head.
The correct plug also depends on the complete combination: compression, cylinder-head chamber volume, fuel octane, ignition timing, ECU or carburetor calibration, cooling-system condition, propeller load, and operating RPM all influence plug temperature.
A colder plug does not make more horsepower, and the coldest available plug is not automatically safer. The goal is to use a plug cold enough to control firing-end temperature under maximum load while remaining hot enough to resist fouling during the engine's actual operating cycle.
Buckshot Racing #77 Recommendation
For Buckshot Racing #77 billet Mercury race heads designed specifically for 3/4" reach plugs, the NGK BR8EIX 6747 is the preferred general-performance starting point for mixed-use and high-performance lake applications.
The NGK BR9EIX 3089 is the colder racing option for higher-compression engines and sustained high-RPM applications such as Mercury Racing 2.4 Bridgeport, 245 Carb, 260 EFI, 280 ROS, 300 Drag and S3000-based builds when the complete engine combination supports that heat range.
Contact Mike Hill at +1-714-697-1716 for tech support.