From what I've seen if you're in the U.S. you're going to want to go with the 2.0 ztech as the spi 2.0 has no viable HP gain and it's basically a commuter engine with a nasty valve seat issue..the ztech has upgrade options..turbos, headers etc..however if yours has a spi you'll need to do a computer swap wiring harness and trans I think. Essentially it's going to be project..mines a stock 2.0 spi with a rebuilt head due to the valve seat issue..won't win any races but it's a good commuter car..Hey guys im considering buying one of the 2.0 spi engines. whats the better engine? the zetec or the spi?? whats the difference in power between the 2 besides the DOHC and SOHc???