if im correct the 1800 zetec engine is 115 bhp an the st is 172, if u want relaibility i woud go for the st engine but neithe engine is as straight forward as a simple engine swp but the turbo build is much more involved an expensive as u need alot of aftermarket bits where as the st u will be able to use stock parts from a scrappy or buy a crashed 1 an sell bits u dont need