How much power the standard ecotec (L36) bottom end can handle, as I am going to be trying to get 400HP atleast, keeping in mind that it is my daily driver.I know it all depends on condition ect.

If you're aiming for around 400hp at the flywheel or around 220rwkw, then it's possible to obtain this figure reliably. In saying this though, there are a number of variables associated obtaining this figure reliably such as engine condition, tune quality and how the car is driven on a consistent basis. If you're committed to running boost through your ecotec then I would HIGHLY recommend running a plenum spacer to improve air distribution in the inlet manifold. As often poor air distribution is main reason that these engine let go is due to pinging of either of the middle cylinders. This is despite people going to the trouble of getting a custom tune done, as AFRs are usually only measured as an average during the tuning process and not based on individual cylinders, hence the problem still occurs unless the air distribution problem is addressed.