Long story short, several years ago, my son brought home this rotor housing from his auto shop class. My son told his shop instructor that I was building a rotary, and since they never touch rotaries in class, the instructor just gave the housing to my son to take home! Anyway, after cleaning the dust off of it, I came to the conclusion that it's most likely from a S4 NA 13B, based on its various distinguishing features (e.g., has the exhaust port diffuser, no bung for a knock sensor, etc.). Since I was building a new 13BT for my S5T2 around that time, this NA housing wasn't particularly useful, so I just put it in storage and forgot about it.

So on the the questions & pictures.
1. Can anyone confirm this is a series 4 NA rotor housing?
2. Is this a front or rear housing? I know Mazda lists different part #'s for the S4 13B NA front & rear housings, but I'm not seeing the expected "F" or "R" marks cast or stamped anywhere on this one. Are these housings interchangeable between front & rear?
3. Given condition shown in the pictures, what would it be worth? Chrome surfaces looks very good & smooth - there's nothing there that can grab a fingernail, no chrome flaking, and the rust stains you see appear to me to be just superficial surface stains that will probably dissolve with good bath in Evaporust. Worst case, I think a housing refinish job would make this one as good as new.



So it's a 13B...

No knock sensor bung, so that eliminates S5 front housings

No groves for the inner/outer seals, so it has to be a post-1985 13B

Exhaust port has the diffuser insert, so it must be an NA housing

Surface near the OMP hole.

Another surface shot near the OMP hole, better view of what feels like just superficial rust stains

Area from exhaust port to leading plug hole

View of surface by both plug holes

 

I seem to recall that S4 housings had the spark plugs located closer together.

Mazda went back to the default spark plug location for the S5 housings.

If you have an S5T2 housing .. that might be fairly easy to check.

 

I'm familiar with the S5T2 housings, and this isn't one of those. The clue is that the T2 housings lack the exhaust port diffuser this housing has. Spark plug location difference is hard to tell visually unless you can put both housings side-by-side, but it's easy enough to measure.

 

This might help:

 

i agree that its an 86-88 non turbo housing.
no water seal, makes it 1986-2003
no knock sensor makes it 1986-1988
no turbo water port, plus exhaust port diffuser makes it an NA

for front or rear there should still be a mark, closer to the metering nozzle port. the only difference i've been able to find between front and rear is the ACV port to "port air" its only drilled on one side for some reason.

 

After a bit more cleaning, I think I found the mark - not the "F" or "R" I was expecting, but the #2. So I'd assume this is a rear housing?

 

that is weird, but sure lets go with that