what is the ratio of the Vortech FMU?
 

as topic
what is the ratio of the Vortech FMU in Greddy kit?

12:1 is stock, as shipped, with the GReddy kit.

Adjustment is done by replacing the disc and spacer inside the unit, as per http://www.vortechsuperchargers.com/...p=31&cat_key=5

if i have replaced fuel pump, do i have to go lower ratio FMU?

Shouldn't have too unless your boost tune was on a weak pump.

Please, Correct me if im wrong.
The 12:1 Disc is the most agressive. So it will depend exactly on Which fuel pump you go with, HP or Not HP, Injector Size Etc. I belive in scotts Faq there is a formula so you can figure out how much Psi of fuel you want at the rail for a certain amount of boost with your chosen injectors. But I dont remember.

Or on a pump that had a much lower maximum pressure. If the 12:1 disc was taking your old pump to its maximum(Like a stock pump would be at ~80psi max), and you added a 190LPH HP pump, you would be running much too much pressure above 5psi of boost or below 12psi of boost.