Stock Compression Applications. Designed for modified engines including performance carburetors, high-flow air cleaners, camshafts, exhaust systems and ignition systems in conjunction with stock compression ratios. Fits '84-'99 Evolution 1340-equipped models, '75-'81 Shovelhead 74 and 80CI models. 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.