It's not about any specific Stage it's about increase or decrease the psi the s/c is putting out therefore bhp
This is for the Harrop TVS
What PSI can I expect from "x" pulley?
64mm / 2.5" ~ 27.5 psi
70mm / 2.75" ~ 25 psi
75mm / 2.95" ~ 22.5 psi
80mm / 3.15" ~ 20 psi
85mm / 3.35" ~ 17.5 psi
89mm / 3.5" 15psi
you will have to search for the M62 look at the http://www.cobaltss.net
Mine came with a 80mm it's running 330bhp (without s/c cams at the moment) when I go 72mm I will increase about 3psi and hope this should push it to 360. But also by going to 89mm it should drop it to the magical 300bhp
300bhp being good because of the requirement not to have to change the pistons for forged, just the rods therefore saving down times and money.