I am a little confused here.I was emailed a quote from a convertor company that said for my combo I should have them build a convertor with a STR around 2.50.I later read on a thread that the higher the STR the less pull on top but it will have more of a hit at low speeds.Can someone please explain?

 

Read this: http://www.converter.com/torqueratio.htm but keep in mind they are windbagging a bit. They are not the only company to use custom stators, nor are they the final word on converters. It does explain the concept a bit. Know this though, the torque muliplication only occurs for a small bit of time, during the flash of the converter as it approaches its "stall speed". It is this function that allows NHRA SuperStock automatics to out ET the stick cars, but not out MPH them. The launch is harder, but the efficiency is less.

 

"Stall Torque Ratio" is a not a concept that is very useful, IMHO. The most sensible definition would be output torque/input torque at stall. But the duration of this condition is just momentary. As soon as the wheels start to move, the conditions change. It's torque over time that moves the car, not torque at one instant. In any case, it's not as though "STR" is independent of the other characteristics of the converter.

I would not try to select or compare converters based on "STR". Also, I don't think there is any standardized method to measure "STR". So, even if it were important, you wouldn't know if one manufacturers claimed "STR" was measured the same way as another's, thus leading to an "apples to oranges" comparison. When I have talked to people at the places that make high end race converters (Coan, Chance, etc.) they never mention "stall torque ratio".

Rich

 

Ya, what he said.