NGK BR6FS SPARK PLUG - 4323

NGK BR6FS Spark Plug – 4323

The NGK BR6FS Spark Plug, stock number 4323, is a proven ignition replacement for a wide range of classic MerCruiser, Indmar, PCM, Crusader, Kodiak, Marine Power, and other GM-based marine engines. Built for dependable performance in demanding boating conditions, this resistor-style plug helps provide quick starting, smooth idle quality, clean acceleration, and consistent power under load.

The BR6FS uses a copper-core center electrode for efficient heat transfer and stable operating temperatures. Durable nickel-alloy firing surfaces provide reliable service life, while the built-in resistor helps reduce radio-frequency interference that can affect marine electronics. Corrosion-resistant shell plating adds another layer of protection in moisture-prone engine compartments.

Worn or fouled plugs can contribute to hard starting, misfires, hesitation, increased fuel consumption, and loss of power. Replacing them during scheduled maintenance helps restore proper combustion and keeps older inboard and sterndrive engines running as intended.

Spark Plug Specifications

• Manufacturer: NGK

• Part Number: BR6FS

• NGK Stock Number: 4323

• Type: Standard resistor spark plug

• Center Electrode Core: Copper

• Electrode Material: Nickel

• Heat Range: 6

• Thread Diameter: 14 mm

• Thread Reach: 11.2 mm

• Hex Size: 16 mm / 5/8"

• Spark Gap: 0.8 mm / .032"

• Resistance: Approximately 5,000 ohms

• Sold Individually

Common MerCruiser Engine Applications

The NGK BR6FS / 4323 is specified for numerous MerCruiser gasoline engines, including select versions of:

• MerCruiser 4.3L V6

• MerCruiser 4.3LX V6

• MerCruiser 5.0L / 305 CID V8

• MerCruiser 198

• MerCruiser 228

• MerCruiser 230

• MerCruiser 5.0L MIE

• MerCruiser 5.7L / 350 CID V8

• MerCruiser 330

• MerCruiser 340

• MerCruiser 350 MAG

• MerCruiser 350 MAG EFI

• MerCruiser 350 MAG MPI

• MerCruiser 400

• Select MerCruiser 7.4L / 454 CID V8 engines

For example, NGK specifically catalogs BR6FS for 1993–1996 MerCruiser 4.3LX engines through serial number 0F802999 and 2000–2006 350 MAG MPI applications through serial number 0F799999.

Other Marine Engine Applications

Depending on year and ignition configuration, the BR6FS is also commonly associated with engines such as:

• Indmar 3.0L GM

• Indmar 4.3L V6 EFI

• Indmar 5.0L V8

• Indmar 5.7L V8 Carbureted

• Indmar 5.7L V8 EFI

• Indmar 5.7L TBI

• Indmar 7.4L V8

• Indmar 7.4L EFI

• Indmar 8.2L V8

• Kodiak 4.3L V6

• Kodiak 7.4L V8

• Select PCM GM-based engines

• Select Crusader GM-based V8 engines

• Select Marine Power GM-based engines

Common Inboard Boat Applications

Compatible GM-based engines were installed in many popular ski, wake, performance, and recreational boats. Depending on model year and original engine package, potential applications include:

Supra

• Supra Comp

• Supra Sunsport

• Supra Saltare

• Supra Mariah

• Supra Pirata

• Select early Supra Launch models

Moomba

• Moomba Boomerang

• Moomba Outback

• Moomba Mobius

• Select early Moomba direct-drive models

Malibu

• Malibu Response

• Malibu Sunsetter

• Malibu Echelon

• Malibu Skier

• Select Malibu Wakesetter models

MasterCraft

• MasterCraft ProStar 190

• MasterCraft ProStar 205

• MasterCraft MariStar 200

• MasterCraft MariStar 225

• Select early MasterCraft X-Series models

Common MerCruiser-Powered Boat Applications

The BR6FS may also be found in compatible sterndrive engine packages installed in boats such as:

• Sea Ray Bow Rider and Sundancer models

• Bayliner Capri and Ciera models

• Chaparral SSi and Signature models

• Four Winns Horizon and Vista models

• Crownline BR and CCR models

• Rinker Captiva and Fiesta Vee models

• Stingray bowriders

• Glastron runabouts

• Larson sport boats

• Regal bowriders and cruisers

• Cobalt runabouts

• Baja performance boats

Cross-Reference Numbers

Common references associated with this application include:

• NGK BR6FS

• NGK 4323

• Mercury / Quicksilver 33-59571B

• Yamaha BR6-FS000-00-00

• Evinrude / Johnson 0509573

• Evinrude / Johnson 0503708

Always confirm an interchange number against the engine manufacturer's specifications before installation.

Key Features

• Genuine NGK BR6FS marine spark plug

• NGK stock number 4323

• Proven application in classic GM-based marine engines

• Copper-core construction provides efficient heat dissipation

• Resistor design helps suppress radio-frequency interference

• Corrosion-resistant shell plating

• Supports dependable starting and smooth acceleration

• Suitable for select inboard and sterndrive engines

• Excellent choice for routine tune-ups and seasonal maintenance

Proven Ignition Performance for Classic Marine Engines

The NGK BR6FS has been used in marine applications for decades and remains a popular replacement for many older GM-based power packages. Its straightforward copper-core design provides dependable ignition performance without unnecessary complexity, making it well suited for classic ski boats, wake boats, runabouts, cruisers, and performance boats.

Whether you're servicing a MerCruiser 4.3LX, 5.0L, 350 MAG, an older Indmar-powered Supra or Moomba, or another compatible GM-based marine engine, the NGK BR6FS Spark Plug – 4323 provides reliable performance from a trusted ignition manufacturer.

Fitment Note: Spark plug requirements can change within the same engine displacement based on year, ignition system, cylinder head, and serial-number range. Boat manufacturers also offered multiple engines in the same hull. Always verify NGK BR6FS / stock #4323 against the engine model, serial number, service manual, or original spark plug before ordering.