These Holley EFI Smart Coils are a bolt-in ignition upgrade for your late model HEMI or Coyote engine. Here's the difference over a stock coil; they produce more spark energy while consuming less power without sacrificing voltage output. This means you get hotter spark at the plug to burn the maximum amount of fuel in each cylinder while using less power from your electrical system. For Coyote or Hemi combinations currently using Holley EFI or Terminator X, use Smart Coil Ignition Harnesses 558-312 & Coil Extension Harnesses 558-326 for a plug and play solution. For new Holley EFI installations on Coyote engines, use with Holley EFI Coyote TI-VCT Main Harness for Smart Coils 558-122 & Smart Coil Ignition Harness 558-312 for a plug and play solution.