When you port the wastegate hole to a larger diameter,you create a situation where the exhaust is allowed to exert its pressure on more square inches of the flapper valve. This causes the valve to open before you want it to. To keep it closed,you need a greater amount of force/spring pressure so you can make more boost. What most people do is to get a high boost actuator. Now you have a new problem which is that you can't lower the boost as much as you might want to. Because of this,I don't use a heavy duty actuator. What I do is install an extra spring externally with the low boost actuator to create more force to keep the valve closed. I drill a small hole in the actuator bracket to attach one end of the spring to. The other end of the spring is attached to the flapper valve crank where the actuator rod is attached. I remove the retaining clip and the extra spring acts as the retaining clip when it is attached to the flapper crank. If I want to run higher boost,I install the extra spring which costs almost nothing. When I want to run lower boost,I remove the extra spring from the flapper crank,let it dangle from the bracket it is attached to and re-install the retaining clip on the flapper crank.
