36-1 Tooth Crank Trigger System for Big Block ChevyHolley's EFI Crank Trigger Kit is engineered to provide an accurate crank speed & position signal to Holley EFI systems in the most demanding, high horsepower, racing applications. Crank position is measured every 10 degrees as opposed to every 45 degrees for a standard 4 Magnet, MSD "style" Crank trigger. It is designed for use on early model BBC Chevy applications using a standard ATI or Fluidamper "style" balancer up to 7 1 4" in diameter.