Denso 5720 Spark Plug

Denso Iridium Racing Spark Plug for Mazda RX-7

The Denso Iridium Racing 5720 is a race-focused spark plug built for serious Mazda RX-7 applications. It combines an iridium center electrode tip with a copper core and a flat-seat design to support consistent ignition performance in demanding trailing-plug use.

Denso’s Iridium Racing line is positioned for no-compromise motorsport and high-output street builds, with construction details chosen for stable spark delivery and durability under elevated cylinder pressure and heat.

Key Features

• Iridium center electrode tip for precise spark delivery
• Copper center electrode core for efficient heat transfer
• Full platinum ground electrode tip design
• Slant ground configuration with one ground electrode
• 5000 ohm resistance
• Manufacturer heat range 31
• Flat seat, 14.00 mm thread diameter, 21.50 mm reach
• Pre-gapped to 0.7 mm
• Compatible with Mazda RX-7 trailing-plug applications

Detailed Description

Denso 5720 is an Iridium Racing spark plug engineered for Mazda RX-7 trailing positions in 1986-1991 and 1993-1995 models. The iridium tip, nickel ground electrode core, and platinum-tipped ground design are selected to maintain stable ignition characteristics in performance engines where plug consistency matters. If you are searching for a Mazda RX-7 trailing spark plug, Denso 5720 provides the fitment and construction details needed for a focused replacement.

This part cross-references DENSO Auto Parts IRE01-31 for the same application.

What It Is Used For

• Replacing a worn or fouled trailing spark plug on Mazda RX-7 rotary engines
• Restoring ignition consistency in high-load or performance driving
• Addressing misfire concerns tied to plug wear or incorrect heat range
• Supporting stable combustion in tuned or modified RX-7 applications
• Maintaining correct plug fitment for trailing ignition positions

Installation Notes and Tips

Fits 1986-1991 Mazda RX-7, trailing; Iridium Racing. Fits 1993-1995 Mazda RX-7, trailing; Iridium Racing. Verify thread diameter, reach, seat type, and heat range before installation. Use the specified gap and follow the vehicle service procedure for rotary-engine ignition service.

Quality Assurance

Denso Iridium Racing components are built for performance-oriented ignition service with material choices that support durability and consistent spark behavior in demanding applications.