The only problem is that SVT and Cosworth already squeezed about as much as they could from the Zetec motor in making the SVT. The only way to make decent power gains is to go forced induction, which it takes to very well.
Mine: 2004 Subaru WRX Wagon: 116k, WRB
Gone: 2002 SVT, #1654
Hers: 2012 Focus Ti Sedan: 67k, SGM, Manual