B&M came up with a modification they called a "Hydro-Stick", which could be held in any gear instead of going into a safety override shift to prevent engine damage. The Dual Range version of the Hydra-Matic could be locked into 3rd. gear for better acceleration in traffic, but it would shift up to 4th. at approximately 65-70 MPH regardless of selector position to prevent valve float due to over-revving of the engine.
B&M figured out how to diasble the safety override, and also modified the vanes on the fluid coupling to allow for higher RPM at the starting line of the drag strip to accomodate radical cam profiles. It was a process similar to the high stall speed torque converters we have now, but Hydra-Matic fluid couplings don't multiply torque at stall speed. The main advantage to a fluid coupling is the fact that they achieve an almost-perfect RPM lockup, instead of the 10% slip that all torque converters have at speed. That's why "lockup" converters are popular now- - - - -they have a mechanical clutch built in to eliminate slippage at light-throttle cruise. (Nothing new about that- - - -Studebaker had a torque converter lockup clutch in 1949!)
Jerry
