High Compression Applications. These plugs are designed for high performance applications involving modifications in high-flow air cleaners, camshafts, exhaust, performance heads, ignition components, higher compression ratios above Original Equipment configurations or engines specific for racing applications. Fits '99-later Twin Cam-equipped models, '86-later XL and XR models, and Evolution 1340 models equipped with Screamin' Eagle Performance Cylinder Heads. Screamin' Eagle ST Spark Plugs feature double platinum coating for superior erosion resistance and extended life. The "V" trimmed ground electrode reduces shrouding of the flame front to promote flame propagation, and the fine wire center electrode enhances start ups and ignitability. Screamin' Eagle ST Plugs feature Ribbed Core Technology (RCT) that provides resistance to fouling, and are designed with Original Equipment-style noise suppression to prevent electrical interference with radios and CB communication equipment. Works great in racing applications where rich air/fuel conditions are required. Unique style with Screamin' Eagle logo.