Denso 5373 Spark Plug

Denso Iridium Power Spark Plug for Exotic Applications

The Denso Iridium Power spark plug delivers precise ignition performance for select high-performance European supercars. Built around a 0.4 mm iridium center electrode, Part Number 5373 is engineered for stable spark delivery and efficient combustion in demanding engines.

Key Features

• Denso Iridium Power line for performance-focused ignition service
• 0.4 mm iridium center electrode for concentrated spark energy
• Tapercut and U-groove ground electrode tip design
• Nickel ground electrode core with copper center electrode core
• 5000 ohm resistance for controlled electrical performance
• Flat seat, 12.0 mm thread diameter, 19.0 mm reach, 18.0 mm hex size
• Pre-gapped to 0.8 mm

Detailed Description

Denso 5373 is part of the Iridium Power product line, a performance-oriented spark plug series built for precise ignition in engines that demand consistent firing characteristics. The iridium center electrode is extremely fine at 0.4 mm, helping concentrate the spark at the plug tip while the tapercut and U-groove ground electrode design supports efficient flame initiation. This spark plug is a direct-fit option for select Lamborghini Diablo applications and Ferrari models including the 348 GTS, Mondial t, 348 TS, Testarossa, and Mondial 3.2. It cross-references DENSO Auto Parts IX27 for the same application.

Vehicle Fitment

• Fits 1991-1999 Lamborghini Diablo, N/A
• Fits 1993-1994 Ferrari 348 GTS, N/A
• Fits 1989-1993 Ferrari Mondial t, N/A
• Fits 1989-1992 Ferrari 348 TS, N/A
• Fits 1985-1991 Ferrari Testarossa, N/A
• Fits 1986-1988 Ferrari Mondial 3.2, N/A

What It Helps Address

• Misfires caused by worn or inefficient spark plugs
• Hard starting from weak ignition output
• Rough idle from inconsistent spark delivery
• Reduced throttle response from degraded plug performance
• Combustion instability in high-output engines

Installation Notes and Tips

Verify thread diameter, reach, seat type, and heat range before installation. Denso 5373 uses a flat seat, 12.0 mm thread diameter, 19.0 mm reach, and 18.0 mm hex size, so matching the engine specification is essential. Check the pre-gap against the vehicle service specification before installation, and inspect ignition components for wear if the engine has a history of misfire or fouling.

Quality Assurance

Denso manufactures the Iridium Power line with a fine-wire iridium center electrode and application-specific construction for consistent ignition performance. Part Number 5373 is built to the listed specifications for the confirmed Ferrari and Lamborghini applications above.