Aussie VT V8 Supercar aero figures

Hi....first time posting in this part of the forum but was hoping someone might have se.leads on the amount of downforce the VT Commodore V8 Supercar was producing back in the day. I have the front spoiler/splitter and rear wing off a car and curious to know what I may need to do re spring rates with this kit bolted onto a car running semi slicks