I have a 1988 turboII with a blown coolant seal. so I am getting ready to pull it and rebuild.
it has 86,000 miles and as far as I know has never been out. car ran grate and had good compression numbers last I checked it ( 100psi or better)
I may do a street port, still thinking about that ( I do have a rtek with 4 720cc already) I bought the 2 dvd's from mazdatrix on rebuilding and how to port
also someone gave me an fd engine (he just got another and swapped them out) but I just took it apart and it looks new in there, WAY nicer than I expected

so my real question is just how much of the fd engine is interchangeable with the s4 engine?
I know I am going to use the rotors and counter weights.
but what about the irons and rotor housings? are they all usable in an fc? ( like I said mine has a blown coolant seal)

I have not taken my engine apart yet, would love for it to look as good as this fd engine but more then likely I will need something.

so what are your thoughts? are there any other parts I need to use as an upgrade?

 

the FD engine has a bunch of upgrades compared to the S4 T2 engine. Basically Mazda upgraded the FD engine to the specs from the racing engines

you should use the FD oil pressure regulator, 110psi vs 71psi. the FD stationary gears and bearings are hardened and multi windowed. the FD front thrust bearings are larger.
the Eccentric shaft has a little extra clearance at the rear of the bearing. the tension bolts have ribs to help with harmonics, and failure.

the rotor housings are essentially the same, except the FD does not have the turbo water holes, and the coating was switched from teflon to graphite (i think, the FD one is better)

the side irons are completely different, Mazda moved the FD intake ports up to make room for the turbos.

the rotors are 9.0 compression, vs 8.5. for less than 450hp, the 9.0 is better, for more than that 8.5 helps. the seals are all the same, except the FD used better corner seal springs.

the FD also has a better CAS, TPS, etc etc