Originally Posted by
ajakeski
You have big ports in the head, more valve lift and probably bigger valves with stock intake and exhaust manifolds. Add the big intercooler to that and that leaves a volumetricly inefficient air pump. The manifolds are restricting the amount of air volume allowed to move through the system. You're basically running a destructor plate.
Large ports and a big intercooler require a large volume of air to be moved through them. The volume of air needs to move at a speed that will allow the entire volume of intake space to fill with air. The turbo helps this process, but will only do so when it is spinning enough to make boost.
A ported exhaust manifold and a large swing valve will allow the turbo to spin up faster. It will also increase the speed of the exhaust gasses exiting the chamber which will help draw more cumbustion air into the cylinder.
There are a lot of other things affecting your system, but it appears the manifolds are the biggest issues.