Assuming you have a standard engine (in your case, with an equal or better flowing exhaust system than that found in a related standard Commodore), then max you can run is 10psi (3.4") - in conjunction with 98 octane fuel. On 95 octane fuel the max you can run is an 8psi (3.6") pulley. With the addition of an intercooler and/or tune, smaller pulleys can be used. This aside, to give you an idea as to the other possible upgrades for your vt supercharged, please refer to the link below.