the FE4 suspension is already more aggressive than the Z51 package.
the sway bars are a larger diameter. 04 ZO6 shocks also include different preloads for gas pressure and were the BEST OEM shocks offered for the C5
What are the differences between the C5 Suspensions? Can I swap them?
Five C5 suspension packages exist:
From GM, each of the five options has its own shocks, springs, and swaybars, all of which are interchangable to make the combination you want.
Sway Bar sizes:
Of the non-adjustable shocks, the only ones worth upgrading to are the '04 Z06 shocks, which have improved rebound damping over previous years. Unless you have the F55 shocks and want to keep them, consider upgrading to these, Konis, or some other aftermarket shock.
Sway Bar sizes:
Sway bars help reduce the amount of body roll your car has in corners. They have a small impact on straight line ride quality as well, but less so than stiffer springs. Larger diameter bars provide more roll resistance.
See FAQ 2-3 for a list of swaybar sizes for C5's.
Upgraded Z06 bars can be had for about $250 shipped from various sources, with bushings and endlinks.
Springs and rates:
Springs keep the car off the ground, and reduce dive/squat during acceleration and braking, as well as controlling body roll. The stiffness goes Base/FE1 < Z51/FE3 < Z06/FE4.
Here are some Spring P/N's, in case you are looking to upgrade:
- Z06 Front spring: 22178729
- Z06 Rear spring: 22188038
- Z51 Front spring: 22178729 (note: same as Z06)
- Z51 Rear spring: 22179020
- Base Front Spring: 22178728
- Base Rear Spring: 22179019
The Z06 rear spring is about 10% stiffer than the Z51 rear - numbers are not 100% known, since the information was not made easily available by GM. Z51 springs are a bit stiffer than F55 springs, which are, in turn, a bit stiffer than base C5 springs.
thanks to http://www.jakelatham.com/c5/misc/faq.shtml#2-1