I have seen that most are very critical on spool so I thought I would post something that I designed and fabricated about 4 years back for a good friend. This is used on an open header when mating to a split flute housing. The idea is to shut off one side of the flute and route all exhaust gas to the other side in an attempt to gain low rpm spool. Once full boost is reached you can then open the other side. This idea is not mine and is used on turbo diesel trucks in Europe. Although the concept netted ~700rpm sooner spool on this setup, I think a turbine housing would need to be specifically designed in order to optimize the results. The shaft, seals and flapper I machined are all designed and made using Hastoloy X. I don't sell this, but perhaps someone can use the concept and apply it to the EVO.