+1 for swaybars, links, tyres.
I run a similiar setup to Joe, (HSD coilovers and the whiteline catalogue), and am very very happy with things now. Took a vehicle (02 Sti) that had bad understeer, (you didnt even need to pushing 100%), to a vehicle thats neutral to slight oversteer bias. (Obviously 'ideal' alignment/toe/castor settings vary person to person too).
Noting you already have the Superstreets, add:
- 22mm front swaybar.
- Spherical end links to suit.
- 24mm rear swaybar. I went blade adjust for both, but you can buy the cheaper ones.
- Heavy duty 'gold' c-links for the rear.
- The XHD chassis mounts.
- An ALK, (either street or race, noting you said you want to track it, and which one depends on your level of comfort/NVH).
- Roll centre adjust kit.
- Additional underbody/in car bracing as required.
If it still doesnt handle then... Get a new driver...
Brent.
