Only the smaller B6 heads are interchangeable with the A series.
The 1.8 BP head is a different beast to the B6 1.6 engine and
its confusing at first but the BP is a larger engine evolution
of the first series b6 1.6 and as a stroke of dumb luck I was able
to see the 2 x 1.8 donks from nissan and mazda can interchange.
I guess Mazda could have looked at the older ca18de.

Are you insinuating that a CA head would bolt to a BP block and visa versa ?
And if so the CA head will bolt to an A series block too as the BP head allegedly does ?

Or have I missed something here

They are almost a match, took a head gasket from mx5 1.8 BP
engine and put it on the ca18de I had and was so close its scary
even oil feed lines up, water galleries and front oil drain
just needs rear drainage like on high hp cadets and fill others.

just in case someone out there wants a better flowing head
with more aftermarket support, better looking and different

Attach file:

---

  mazda bp 1.8 and ca18.jpg (80.17 KB)


  mazda bp 1.8.jpg (109.78 KB)