Alot of people will drill out the puck hole, but I feel this is a band-aid approach. I have my own theory as to why boost spikes happen in some cases. The boost finds its way to the wastegate diaphragm and opens it. If the rate of pressurization (rate of flow into the wastegate diaphragm) is correct, the puck will open when it should and you wont see a spike. But if it takes longer than it should for the wastegate to pressurize, then you will see more boost than you should for a moment, and then the wastegate will reach max pressure, and then open the puck more, bringing the boost back down. The restrictor in the Y fitting may not allow enough air to flow into the wastegate fast enough...in the case of a system that spools faster than stock. The GM engineers designed this fitting with the hole size just right, to allow the rate of flow to fill the wastegate completely right at the moment you reach 14.7psi. Basically, I would experiment with opening the hole in the Y-Fitting slightly...maybe 10%, and see what that does for spikes. This may end up dropping your boost, but it would just be a matter of turning it back up. And in the end, the spike will probably be gone.
