A Standard Small Turbo Escy Engine.

Is it just the turbo and management?

Or is the head a worse design?

Can someone explain to me please.

Basically would i be able to bolt a bigger turbo on and l8 or S8 and achieve 400bhp?

Or will the head only flow say 330 in standard form?, im aware that when worked it can flow much more, i.e Gaybirds engine or Yums etc etc.

I take it these engines themselves are pretty good though?