To see how hot things are actually getting, install an exhaust gas temperature gauge / pyrometer, and install it pre-turbine. Stock 1.6lTD peaks at 1500 deg. F pre-turbine, and you'll want to have yours peak considerably cooler. I've had the VNT 1.6D heated up to 1400 deg. F before (that was tested before it was intercooled), and although it survived, I'd recommend taking a conservative approach to tuning yours and staying well below that.