Sold in set of 8. 

Economical performance and improved ignitability over standard NGK Spark Plugs original equipment manufacturer and racer approved.

• Lowers ignition system voltage requirements

• Greater ignitability and performance over conventional spark plugs

• Trivalent Metal Plating has superior anti-corrosion and anti-seizing properties

• Increased fuel economy and lower emissions

• Highly durable against electrical and chemical wear

• Good performance spark plug

The TR55 is recommended for GTs. It can be used on near stock GTPs but we recommend a colder plug for boosted applications.
The TR6 is our most popular plug. It is well suited for 3.4" pulley'd Grand Prix. This plug will give you full mileage and doesn't require any special precautions for use.
When eliminating KR is top priority, when changing your plugs every 6k miles isn't an issue, or when you must push the limits of performance the TR8 race plug does the trick. It is 4 heat ranges colder than stock.


Iridium IX Spark Plugs (shown in bottom pictures) are the most technologically advanced high performance plugs available. Featuring a 0.6 mm iridium center electrode tip, they offer superior ignitability without sacrificing durability. The tapered ground electrode increases flame kernel expansion, while the superior heat range design is ideally suited to the demands of high performance environments. Specially designed to meet the needs of serious enthusiasts, Iridium IX Spark Plugs offer outstanding acceleration, high fuel efficiency and long life. When you demand the most from your engine, rely on the proven performance of NGK Iridium IX Spark Plugs.

Iridium plugs burn clean and a colder range of plug can be used without the normally associated risk of plug fouling. TR55ix's are recommended for non boosted applications. TR6ix plugs recommended for low boost applications. The Iridium line of plugs are designed for maximum performance with maximum life. They will last 50k miles plus and perform better than the standard NGK plugs.
Iridium plugs cannot be gapped. The tip is too delicate for the gap to be changed. For those brave and wanting to try and regap, here are some tips from Denso http://densoiridium.com/installationguide.php