no it's not a torque converter, you already have one if your'e running an automatic.( they're the big donut lookin' thingy) a shift improver kit is just a different way for the fluid in the tranny to be routed (other than the stock or factory valve body) it looks like a thin sheet of sheetmetal w/ lines and curly q's.....go to
www.summitracing.com look up prt. #bmm-30262. or if you want to see what else they have by other manufacturers, along the left side margin under "key word search" ....put in "shift improver kits". just look for your application.....th350,th400.....etc.
