Can someone explain to me what spiking is? Thanks!

 

Spiking is where the wastegate cannot expell the excess exhaust gas fast enough, so the turbocharger creates more boost. This can be solved by making the actual wastegate opening larger. This can be achieved by either a) buying a larger wastegate (if you're dealing with an external wastegate), or porting the wastegate housing and "flapper" area (if it's an internal wastegate).

Hope that helps.