Cylinder wall thickness

[greenamex2]

How thick is 'thick enough' for a cylinder wall?

Details as follows -

- Cast iron block, no liners (Toyota 4a-ge).
- 82mm bore (currently, hence the question).
- 77mm stroke (will probably end up a couple of mm longer).
- 9500RPM.
- 220BHP (want more).

Cuurently the minimum wall thickness is around 4mm, am I pushing going out any further?

There is a bunch of stuff regarding this engine on the internet but most of it is cobblers so I tend to ignore it.

Thanks.