Lots of differences. the zetec se is the 1.25, 1.4, 1.6 and sort of 1.7 (it's a variation of the se engine) as fitted to the focus, puma, fiesta etc. The zetec e and zetec r (plus duratec st170 and focus rs versions) are a completely different engine available in 1.6, 1.8 and 2.0. It may be worth a look at burton powers website if you need to know more, as they have a small write up on each engine.