Some of the mods I did on my 10v gave a really good improvement to the car. In the engine bay, I moved the battery to the boot and fully stripped out all the A/C system and lots of needless trims, headlamp washers, basically anything that wasn't essential I removed it. Lost 46kg over the front axle (gained 20kg over the rear axle). This massively improved the balance of the car during cornering.
I also fitted a 6-speed gearbox from a GT 1.9 JTD, with a Q2 limited slip diff. The 6-speed box made the 2.4 a lot punchier in 2nd through to 5th and the 6th gear was usefully lower revving than the previous 5th, so eventually it would have paid for itself in better fuel economy. The LSD is the single best thing you can do to improve grip and handling.
If you haven't already, some 17" wheels with good 225/45/17 tyres fitted.
Eibach anti-roll bars - these keep the car really planted through the corners instead of leaning over. Big improvement on standard. Brembo 4-pot front brakes work well too.
Thats about all I can think of for now!
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