S2000 performance upgrades?

[caduceus]

I currently have a TVR Cerbera 4.5, but looking to change, and the S2000 is high (if not top) on my list.
A 400bhp (alledgedly) to a 240bhp is quite a drop, so I'm wondering what kind of upgrades are available. Without going down the forced induction route.
I have seen posts on Bibbs car which sounds like a beast. But I just want to know how much more bhp/torque can be extracted from the S2k.

Thanks
Cad