Curb weight depends heavily on drivetrain. A base four-cylinder car with a manual sits around 2,900 lbs. A loaded IROC-Z with the 350, automatic, T-tops, and power everything pushes past 3,400 lbs. T-top cars are heavier than hardtops and structurally weaker (more on that below). If you're building one for performance, the hardtop with a manual is the lighter, stiffer starting point. Subframe connectors are almost mandatory on T-top cars to reduce cowl shake.