hes talking about the greddy cores, the 24 is the biggest of the two. if you gotta chose between either two i'd go for the 24, not sure which one was the better one though, the V or the R, its been a while since i read up on them. but from i read up, its better to get a kit with shorter routed piping, greddy goes the long way around (slightly longer spool up, longer pipes to fill up before it gets to the engine) and i heard that their cores arent too sturdy.