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Description

NGK BR8HS-10 Spark Plug 1134

The NGK BR8HS-10, NGK Stock No. 1134, is a resistor-type spark plug used in select marine and 2-stroke applications, including compatible Johnson/Evinrude outboards.

Its short-reach design, resistor construction, and NGK heat range 8 make it a useful option for engines that require a conventional electrode plug with a 1.0 mm (.040″) factory gap.

For racers and performance users, the BR8HS-10 is especially useful when comparing plug heat ranges because it is one step hotter than the BR9HS-10 while maintaining the same basic physical configuration.

Spark Plug Specifications

• Manufacturer: NGK
• NGK Part Number: BR8HS-10
• NGK Stock Number: 1134
• Thread Diameter: 14 mm
• Thread Reach: 1/2 in. / 12.7 mm
• Hex Size: 13/16 in.
• Seat Type: Gasket
• Resistor Type: Yes
• NGK Heat Range: 8
• Factory Gap: 1.0 mm / .040 in.
• Electrode Style: Standard
• Center Electrode Core: Copper
• Ground Electrode Material: Nickel

What BR8HS-10 Means

The NGK part number gives useful information about the plug:

• B – 14 mm thread diameter
• R – Resistor spark plug
• 8 – NGK heat range 8
• H – 12.7 mm / 1/2-inch reach
• S – Standard electrode design
• -10 – Factory gap of 1.0 mm / .040 inch

This makes it easy to compare the BR8HS-10 with similar NGK plugs that differ only in heat range or gap.

BR8HS-10 vs. BR9HS-10

The BR8HS-10 and BR9HS-10 share the same basic dimensions and resistor-style construction, but the heat range is different.

BR8HS-10

• Heat range: 8
• Runs hotter at the firing tip

BR9HS-10

• Heat range: 9
• Runs colder at the firing tip

With NGK plugs, a higher number means a colder plug. The hotter BR8HS-10 can help resist fouling in an engine that does not generate enough combustion temperature for a colder plug, while the BR9HS-10 may be preferred in engines operating under heavier sustained load or higher combustion temperature.

Plug heat range should always be matched to the engine and operating conditions rather than selected simply because one plug is considered “hotter” or “colder.”

Stock Johnson/Evinrude Applications

The BR8HS-10 is used in select Johnson/Evinrude and other marine applications that call for a short-reach, resistor-type plug in this heat range.

Because OMC used different spark plugs across engine families, ignition systems, and model years, always verify:

• Engine model
• Recommended heat range
• Required plug gap
• Thread reach
• Resistor requirement

SST-45 / Formula Light Considerations

For SST45 / Formula Light racers, the BR8HS-10 can be useful as an alternative heat-range option when the engine setup or operating conditions call for a slightly hotter plug than the BR9HS-10.

At Liquid Revolutions, spark-plug condition is one of the quickest ways to compare how the cylinders are running and to spot changes in combustion, fuel delivery, or ignition behavior.

The BR8HS-10 may be worth considering when:

• A colder plug is fouling
• The engine spends more time at lower load
• Plug temperature appears too low
• Tuning conditions favor a slightly hotter plug

A hotter plug does not create more spark or more horsepower. The difference is how quickly the plug transfers heat away from the firing tip.

Why Heat Range Matters

The spark plug needs to stay hot enough to burn off deposits but cool enough to avoid overheating.

A plug that runs too cold can contribute to:

• Carbon fouling
• Oil fouling
• Misfiring
• Difficult starting
• Poor low-speed operation

A plug that runs too hot can contribute to:

• Electrode overheating
• Pre-ignition risk
• Abnormal combustion
• Excessive plug wear

The correct heat range depends on the engine, compression, fuel, ignition, load, and operating conditions.

Why the Resistor Matters

The R in BR8HS-10 indicates an internal resistor.

Resistor plugs help reduce electrical interference from the ignition system and are commonly used with electronic ignition systems.

This can help reduce noise affecting:

• Ignition electronics
• Gauges
• Data systems
• Radios
• Other onboard electronics

Spark Plug Gap

The -10 designation indicates a factory gap of approximately: 1.0 mm / .040 inch

Always check the gap before installation.

Shipping, handling, or previous adjustment can alter the gap, and some engines may require a specification different from the factory setting.

For performance and racing engines, use the gap appropriate for the actual ignition system and engine setup.

Common Signs a Spark Plug Should Be Replaced

Inspect or replace the plug if you find:

• Heavy carbon deposits
• Oil fouling
• Fuel-wet electrode
• Rounded electrodes
• Cracked porcelain
• Damaged threads
• Corrosion
• Excessive deposits
• Signs of overheating
• Intermittent misfire

A fresh plug is often one of the simplest ways to eliminate a variable during ignition troubleshooting.

Reading Spark Plugs on a 2-Stroke

Spark plugs can provide useful information about cylinder-to-cylinder differences.

Compare the plugs for:

• Color
• Deposits
• Fuel wetness
• Oil buildup
• Electrode condition
• Signs of excessive heat

A plug that looks noticeably different from the other cylinder may point toward an issue with:

• Carburetion
• Fuel delivery
• Ignition
• Compression
• Cooling

Plug appearance should be used as one diagnostic tool alongside proper engine testing.

Key Features & Benefits

• NGK Stock No. 1134 – Genuine BR8HS-10 identification
• Heat Range 8 – One step hotter than BR9HS-10
• Resistor Design – Helps reduce ignition-related electrical interference
• 14 mm Thread – Common marine spark-plug size
• 1/2-Inch Reach – Short-reach configuration for applicable cylinder heads
• 13/16-Inch Hex – Standard service size
• Factory .040″ Gap – BR8HS-10 wide-gap configuration
• Marine & Performance Use – Suitable for compatible Johnson/Evinrude and 2-stroke applications

Installation Tips

Before installation:

• Confirm the correct part number
• Check the spark-plug gap
• Inspect the plug boot and wire
• Start the plug by hand
• Avoid cross-threading the aluminum cylinder head
• Tighten to the correct specification for the engine

If the plug does not thread smoothly by hand, stop and inspect the threads before using a wrench.

For racing applications, choose the heat range based on the actual engine setup and operating conditions rather than assuming the BR8HS-10 and BR9HS-10 are interchangeable in every situation.