Econo Performance Torque Converters BM400004Econo Performance Torque ConvertersSuit TH400 & TH350, 3500 3800 rpm, 10. 75" bolt circle BM400004 400004 These Converters are budget priced and are intended for mild street engines up to 350 horsepower. They should not be used with nitrous, superchargers or transbrake but are perfect for street cars and hotrods. Stall speeds are based on an engine producing 230lb ft of torque at 2500 RPM. Engines with more torque will stall higher and less torque