I went on autozone.com to look up coil springs for my project, i just want the heavier duty springs. i find at least 3 different part numbers for Shelby and Turbo Z with prices from 58.99-66.99- 100.99. my question is what car came with the heaviest duty springs? they dont have the iroc or r/ts, just the 86 turboz and shelby from 89-91 listed