NGK 97921 Spark Plug

NGK Iridium IX Spark Plug for Performance Ignition

NGK Iridium IX Spark Plug 97921 is built for drivers who want precise ignition response, stable idle quality, and durable service in modern performance engines. This NGK Iridium IX Spark Plug uses a fine-wire iridium center electrode, a tapered cut ground electrode, and a resistor design to support clean firing and consistent combustion.

Compatible With select Cadillac CT4, ATS, CTS, and XTS applications, as well as Ford F-150 and Mustang models listed below, this plug is a direct-fit ignition service part for the specified engine applications. Part number 97921 is also identified by service number LTR7AIX.

Key Features

• Iridium fine-wire center electrode for durable spark delivery
• Taper cut ground electrode for improved starting, idling, and throttle response
• Single iridium metallurgy with a copper core center electrode
• Resistor type design with 5,000 ohms resistance
• Pre-gapped at .032 in. / 0.8 mm
• M14 x 1.25 thread, 0.984 in. reach, 5/8 in. hex
• Manufacturer heat range 7 with tapered seat construction

Product Details

NGK’s Iridium IX line is aimed at performance-focused ignition service, combining a fine-wire iridium center electrode with a tapered cut ground electrode to promote reliable ignition under demanding conditions. The iridium alloy’s high melting point and the plug’s anti-fouling characteristics help maintain consistent operation in engines that benefit from a stable spark and efficient combustion. For shoppers comparing ignition parts, NGK 97921 is a practical choice for service on Ford Mustang and Ford F-150 applications, along with the listed Cadillac models.

This part cross-references Dorman - HELP (e.g., 97921) for the same application.

What It Helps Address

• Hard starting caused by worn or inconsistent spark plugs
• Rough idle from degraded ignition performance
• Throttle hesitation during acceleration
• Misfire symptoms related to plug wear or fouling
• Reduced fuel efficiency from weak spark delivery

Installation Notes and Tips

Verify the specified gap before installation and follow the vehicle service information for torque and plug replacement intervals. This plug uses a tapered seat, M14 x 1.25 thread size, and a non-removable nut terminal. Confirm the application by year, make, model, and engine specification before ordering. Fits 2025 Cadillac CT4, N/A; Fits 2022-2024 Cadillac CT4, N/A; Fits 2016-2019 Cadillac ATS, N/A; Fits 2015-2019 Cadillac CTS, N/A; Fits 2016-2019 Cadillac XTS, N/A; Fits 2023-2024 Ford F-150, N/A; Fits 2022 Ford Mustang, N/A; Fits 2019-2021 Ford Mustang, N/A.

Quality Assurance

NGK is a recognized ignition component manufacturer, and the Iridium IX design is engineered for durability, stable ignitability, and consistent performance in the listed applications. Part number 97921 / LTR7AIX is specified for the fitments shown above.