My buddy has a 2003 focus with the SPI sohc motor and would like to get
some more performance out of it. Lots of parts available for the zetec
motor, but not for the SPI. My question: what is part interchangeability
between the two engines like? also, are there differences in the intake
manifold/throttle body setup between the two engines and could a dohc
header be made to fit a sohc cylinder head? Thanks in advance for your
The blocks are the same but there are many differences in the heads etc. You
can get a lot of information on such specialist sites as Focus Fanatics at
My guess is that unless your buddy is especially attached to his 2003, his
best option is to be content with keeping it in good tune i.e. plugs, fuel
filter, injector cleaner, clean the intake plenum etc. Also, a
lower-restriction exhaust and air filter may help. Beyond that, I think he
would be better off trading it for a Zetec. It would be much less trouble
and expense than attempting to mod an engine designed for economy and
durability, not speed.
Me, I'm really happy with the pep of my 5-speed SPI. But then I'm an old man
and drive like one... uh, mostly :<)
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