Hi I'm thinking on converting my si. The obvious option is a 2.0 swap but i've been told that an xr2i 1.8 head could fit my 1.6 block? Has anyone done/heard this? Apparently the valves are too small to get anything decent out of the 1.6 16v head but the 1.8 16v head is better?
Thanks.

In theory it will fit,
the 1.8 head shares the 2.0 larger valves so flows better (the 1.6 valves are like chocolate buttons)
the blocks are practically the same
the compression might be lower with the standard ford headgasket but you can fit the early (1998-1999( focus mls head gasket
which is half as thick and should bring the compression in line.

i had a spare xr2i 16v head but the theiving gypsie pikies stole it off my drive along with the incredably hard to find rs1800 throttle body and not so hard to find HO manifold)

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buttery biscuit boost

1.8 and 2.0 head won't fit the 1.6 i believe.

wouldnt even bother messing with the 1.6 lump just drop in a 1.8 or 2ltr

i've heard that sticking a 1. 8 head on a 2.0 block increases the compression ratio so in a sense good for small time racers etc. but 1.8 on 1.6 to me sounds like kabooom! in a fiesta its so easy to do an engine conversion!! if you want because 2.0's are so sort after, get a 1.8 115ps engine from an escort or mondeo more common to find, add 2.0 cams etc and you should have a good bhp figure!