NGK 6637 Spark Plug - Intake Side

NGK Iridium IX Spark Plug 6637

NGK Iridium IX Spark Plug 6637 is built for drivers who need precise ignition performance and dependable service life. With an iridium center electrode, copper core, and 5000 ohm resistance, this plug is engineered for stable spark delivery across a wide range of older import and domestic applications.

Compatible With select Porsche 911, Volkswagen Jetta, Volvo 740, and Mitsubishi Eclipse applications, this NGK spark plug is a direct-fit ignition service part for many classic and late-1980s to 1990s vehicles. The BPR6EIX configuration also appears in cross-reference listings for select OE and aftermarket applications.

Key Features

• Iridium center electrode tip for consistent ignition performance
• Copper core center electrode for efficient heat transfer
• Nickel ground electrode with taper-cut tip design
• 5000 ohm resistance for radio-frequency suppression
• Flat seat design with 14 mm thread diameter and 13/16 in. hex
• Pre-gapped at .032 in. for many listed applications; some vehicles require a different gap

Product Details

NGK’s Iridium IX line is part of the brand’s performance-focused spark plug family, backed by more than 80 years of ignition expertise and OE supply experience. Part number 6637, also identified as BPR6EIX, uses an iridium firing tip to support reliable spark consistency while the copper core helps manage heat under normal operating conditions. The removable nut terminal and standard ground configuration make it a practical service replacement for a broad range of vehicles, including Porsche 928, Volkswagen Golf, and Land Rover Discovery applications listed in the fitment data.

This part cross-references Monroe Shocks & Struts (e.g., 5502) for the same application.

Common Issues This Part Can Address

• Hard starting caused by worn or fouled spark plugs
• Rough idle from weak or inconsistent ignition output
• Misfire conditions related to degraded plug electrodes
• Reduced throttle response from aged secondary ignition components
• Maintenance replacement for vehicles calling for NGK BPR6EIX / 6637

Installation Notes and Fitment Tips

• Fits 1994-1999 Land Rover Discovery, N/A
• Fits 1990-1999 Mitsubishi Eclipse, N/A
• Fits 1991-1995 Volvo 940, N/A
• Fits 1984-1992 Volkswagen Jetta, N/A
• Fits 1984-1989 Porsche 911, N/A
• Fits 1986-1989 Nissan D21, Intake Side
• Fits 1987-1988 Nissan Pathfinder, Intake Side
• Fits 1985-1991 Porsche 944, N/A

Verify the specified gap before installation. Listed applications call for different settings, including .032 in., .028 in., .025 in., and .024 in. depending on vehicle and engine configuration. Use the correct gap for the exact year, make, model, and position shown in the fitment data, especially on dual-plug Nissan applications and older Porsche, Volvo, and Volkswagen engines.

Quality Assurance

NGK is a major OE spark plug supplier in North America and manufactures ignition components for domestic and import vehicles, motorcycles, marine engines, and small engines. Part number 6637 reflects NGK’s OE-focused manufacturing standards and broad application coverage for service replacement use.