You need Acrylic Enamel Reducer, not Enamel Reducer. I painted a 383, 15 years ago with Delstar without use of the hardner, and it still looks great. It is debateable whether or not to use a hardener. It is not required to make the paint cure. It does increase duarability and shine, and allow for polishing as on the exterior of a car. The finish with the hardner is really too shiny to look correct on an engine, and causes the paint to be somewhat brittle.