Me and my codriver have done four local events and one very wet, very cold test and tune. I am convinced that the GXP can be competitive on a national level, but it absolutely needs both a stiffer front bar and better shocks. And here's why:
The car has too little roll stiffness in the front. This is amplified by the soft (almost non-existant) low-speed damping the stock shocks exhibit. If you drive the car super smooth it can be fast, but once you overshoot a mark, it takes a really long time for the car to recover. Also, with the current alignment (which i'm not super happy with) the car exhibits some loss of rear traction under power, which the stiffer bar will also help.
I really don't you can compare the ZOKs and GXPs they are really different animals, and what works on the ZOKs may not work at all on the GXPs. I think the GXP needs to be stiffer than it currently is and the shocks and bar will help that.
Also the car really needs to have a good alignment.
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If you can't be a good example, be a terrible warning!
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Current Stable:
1998 Toyota FJ62 "Bruce"
2006 VW Mk5 GTI DSG "Ingraine"
2007 Mean GXP, Team Zissou!