I put the stiffest springs that are available for our cars (standard rates on front, stiffest)
and progressive rates on back (intrigue) and the car doesn't sag at all with approx 800lbs of DJ equipment in it. it actually sits just like stock ride height new. I also got AGXs and when it's empty it rides a bit stiffer than stock (when turned down), and when I'm loaded, I turn them up. only possible downside of the combo is when the car is empty, the car tends to sit about an inch higher in the rear than in the front. not noticable to anyone but a fellow GPer, though
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98 GTP GMPP handling kit, HomemadeFWI, MSD coils, Taylor wires, 180 drilled tstat, TR6IX plugs, Intense STD PCM, JimmyC DP, Thrasher shift kit (mild setting), AGX/Intrigue spring setup, drilled/slotted rotors with Hawk HPS pads. Hopefully more to come