At one point it was rumored that the USDM Corollas had stiffer valves springs compared to the GR Yaris. We have recently proven this to be false. This should be the first engine modifacation done as it is the first limiting factor when tuning. Before the stock turbo is maxed out, valve float at high RPM occurs. Heres the "Drop in" solution. We highly suggest these to be installed by a professional.
