7. Our converter of choice for this project is the Circle D Specialties Pro Series Stage III 258mm converter (PN 38-13-05). It features a custom CNC, billet-aluminum front cover and your choice of five stall speeds, ranging from 3,000 to 4,000 rpm. We chose the 5C, the 4,000-to-4,200-stall version. This will allow us to launch at a higher rpm, which will help our 60-foot times tremendously, and we’ll be able to take full advantage of the higher operating range of the cams.