Is this what I need for more boost?

I couldnt get my blower to boost past 5 so i think I got some gigantic pulley on it instead of stock so I was wondering if this is the one i need?

Im in france so i cqnt get a exact measurement but it was bigger then 3.5 inches so i figure its a downgraded pulley. Im in france and its hard as hell to type anything/read anything but ill post a pic of the bllower pulley in a sec. ANy other idea ahy im only making 5#s?
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