Hays torque converters?

I get that. I just don’t know what the deal is with diameters vs what there used for and in. I do know that faster cars will have smaller converters. Less fluid inside to move? Would be the reason I guess.

Maybe, maybe not. The way converter technology is now, a faster car may or may not use a smaller converter. It all depends on what the best match is for the given combo. At least in THIS day and time. Used to be what you said was true across the board. Smaller diameter converters were used in faster and faster cars. Now, not so much.