What challenges will I have to face if I want to machine a 3-speed automatic with a high-lockup torque-converter, and pair it with an `Iveco 2.3 HPi` engine? With a transmission like this, it's really the torque converter that will be keeping the engine rpm within the useful part of the powerband, not so much the transmission's gears. On paper, the torque converter will need a rather hefty 12-inch diameter, a 4:1 stall ratio, and a lockup-rpm of 2400. Obviously, this is likely subject to change in practice. The 3 gears will more or less be a "launch gear," "direct gear," and an "overdrive gear," being ratios of 3.23:1, 1:1, and 0.63:1, on a final drive of 4.33:1. This will be installed into my small featherweight car heavily inspired by cars such as the "Caterham 500" and the "Ariel Atom."