Because the Turbo 400 is a bigger, beefier version of the GM TH-350, this added strength comes with increased rotating weight and mass of its gears and internal components. As all good racers know, weight and mass absorbs horsepower produced by the engine, and those stronger, wider gears increase what the engineers refer to as “parasitic loss”, due to greater friction. Just how much power is sacrificed to a TH-400 over, say, an aftermarket design, two-speed Powerglide varies by application. Despite this shortcoming, when power and torque exceed the capability of an automatic transmission to resist component failure, the answer is often found in a Turbo 400. It’s also still reasonably easy to locate a used Turbo 400 transmission core as a starting point, and the cost of a racing rebuild is also still attractive.