An aftermarket assembly designed to enhance the General Motors Turbo Hydra-Matic 400 (TH400) transmission by incorporating an additional gear ratio. This addition effectively reduces the engine’s revolutions per minute (RPM) at cruising speeds. For instance, a vehicle equipped with a TH400 and a 4.10 rear axle ratio might experience significantly lower engine RPM at 70 miles per hour after the system’s installation, compared to its previous state.
The implementation of this assembly offers several potential advantages. A primary benefit is improved fuel economy, as the engine operates at a more efficient RPM range during steady-state highway driving. Furthermore, reduced engine wear and noise levels can contribute to a more comfortable and potentially longer-lasting vehicle. Historically, this type of upgrade has been particularly attractive to owners of classic cars and trucks originally equipped with TH400 transmissions, seeking to modernize their vehicles’ performance without sacrificing the robustness of the original transmission.
