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Description

The NGK BPZ8HN-10, NGK Stock No. 4495, is a marine spark plug designed for select 2-stroke outboard applications that call for a projected firing-end, resistor-type plug.

That design places the spark farther into the combustion chamber and can improve ignitability while helping resist fouling when used in the correct engine.

Spark Plug Specifications

• Manufacturer: NGK
• NGK Part Number: BPZ8HN-10
• NGK Stock Number: 4495
• Thread Diameter: 14 mm
• Thread Reach: 1/2 in. / 12.7 mm
• Thread Pitch: M14 x 1.25
• Hex Size: 13/16 in. / 21 mm
• Seat Type: Gasket / Crush Washer
• NGK Heat Range: 8
• Factory Gap: 1.0 mm / .040 in.
• Firing End: Projected
• Center Electrode: Copper-core
• Ground Electrode: Nickel
• Marine Cross Reference: Champion QL78YC

What Makes the BPZ8HN-10 Different?

The key difference is the projected firing end.

Compared with a conventional short-reach plug, the BPZ8HN-10 positions the firing tip farther into the combustion chamber.

This can help provide:

• Improved ignitability
• Better flame initiation
• Reduced tendency to foul
• More consistent combustion
• Improved low-speed plug cleanliness in applicable engines

That does not mean a projected-tip plug should be substituted into every engine that accepts the same thread size.

The combustion chamber must be designed for the additional tip projection.

BPZ8HN-10 vs. BR9HS-10

The BR9HS-10 differs in two important ways.

BPZ8HN-10

• Heat Range: 8
• More specialized marine design
• Common Champion cross reference: QL78YC
• Hotter than a heat-range 9 NGK plug
• Projected firing end

BR9HS-10

• Heat Range: 9
• One NGK heat range colder
• Standard firing end
• Common Champion cross reference: QL78C

With NGK plugs, higher numbers indicate colder heat ranges. So a BR9HS-10 transfers heat away from the firing tip faster than the BPZ8HN-10.

Marine & Outboard Applications

The BPZ8HN-10 is used in a number of marine 2-stroke applications, particularly engines designed for a projected-tip plug.

It is commonly associated with select:

• Mercury outboards
• Mariner outboards
• High-performance 2-stroke marine engines
• Other engines specifying Champion QL78YC or an equivalent plug

Because spark plug requirements depend heavily on cylinder-head design and ignition configuration, always verify the exact engine recommendation before installation.

Champion QL78YC Cross Reference

One of the most useful cross references for the BPZ8HN-10 is:

Champion QL78YC

This makes the NGK 4495 a common alternative where QL78YC is specified.

As with any cross-reference, verify:

• Thread size
• Reach
• Heat range
• Tip projection
• Gap
• Manufacturer recommendation

before substituting plugs.

Why Heat Range Matters

The BPZ8HN-10 uses NGK heat range 8.

A spark plug must stay hot enough to burn off deposits but cool enough to avoid overheating.

A plug that runs too cold may contribute to:

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

A plug that runs too hot can increase the risk of:

• Electrode overheating
• Pre-ignition
• Abnormal combustion
• Accelerated plug wear

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

Common Signs a Spark Plug Should Be Replaced

Inspect or replace the plug if you find:

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

A fresh set of plugs is also useful during ignition troubleshooting because it removes one variable from the diagnostic process.

Performance & Racing Considerations

For performance outboards, spark-plug selection becomes more important because the engine may operate at sustained high RPM and heavy load.

At Liquid Revolutions, we look at spark plugs as both an ignition component and a diagnostic tool. Plug condition can help show differences between cylinders and may point toward fuel, ignition, compression, or cooling issues.

The projected-tip design of the BPZ8HN-10 can be beneficial in engines designed for it, but it should never be installed simply because the thread size matches.

Projected plugs extend farther into the combustion chamber, so proper engine compatibility is essential.

For an SST-45 or other modified racing engine, use only the plug style, heat range, and gap appropriate for the specific cylinder head and engine setup.

Key Features & Benefits

• NGK Stock No. 4495 – Genuine BPZ8HN-10 identification
• Heat Range 8 – Suitable for demanding marine applications when specified
• Projected Firing End – Helps improve ignitability and resist fouling
• 14 mm Thread – Common marine spark-plug size
• 1/2-Inch Reach – Short-reach marine configuration
• Factory .040″ Gap – Supplied with a 1.0 mm gap designation
• Copper-Core Center Electrode – Supports consistent heat transfer
• Champion QL78YC Cross Reference – Useful for applicable marine engines

Do not substitute this plug for a standard non-projected plug unless the engine manufacturer or your specific engine setup calls for it.