NGK 3689 TR6IX IRIDIUM SPARK PLUGS 1 HEAT RANGE COLDER FORD SVT 99-04 LIGHTNING, 99-04 COBRA 02-03 HARLEY SUPERCHARGED (8)

• Iridium IX Spark Plugs are the most technologically advanced high performance plugs available. 
• Featuring a 0.6 mm iridium center electrode tip, 
• 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. NGK's new Iridium IX is the personification of these qualities and takes premium performance spark plugs to a new level. A level that is expected from the world leader in spark plugs.

LFP reccommends upgrading to a colder spark plug such as the TR6 when adding more boost.