Alright I got these parts recently and I cant' tell if they are S4 or S5. I was told they were all S4 TII and all stock. But I've alreayd figured out that the motor was poryted. LOL Everything was ported when I compared them to my stock parts. And then these housings have numbers on the top of them that my other housings don't have. What do they stand for? And also how can I tell if I have S4 or S5 internals like housings and all. I have my original S4 TII rotors and eccentric shaft so I'm not worried about those but everything else. Does it actually matter? And a housing is missing a stud(?). Where can I buy a replacement?

 

That is an atkins rotary rebuild stamp...thus the ARS at the end. It was an 8/97 build date.

I cant tell if they are s4 or s5 housings, but really it doesnt matter, you can use either in any 86+ rotary build so long as they are both the same in the same engine (no mixing and matching). If they are s5 there will be a knock sensor threaded hole/casting above the trailing plugholes. If they are series 4 there will be a flat "name plate" cast into the top of the rotorhousing that says "mazda motors hiroshima japan".

An s4 front iron has a small casting for the front cover o-ring...the s5 has the larger casting. The s4 intermediate is about the same as the s5 other than the s5 having a later opening port (smaller). The s4 rear appears the same as the s5 in most cases, but a few s5 rear irons have the reinforcement at the oil filter pedestal. All s5 rears have the larger diameter hole for the coolant temp sensor, while most s4 rears have the smaller hole...there were a few late s4's with the large hole here, though.

s5 turbo f/r irons have 1/16" wider intake ports (where the LIM bolts on) than the s4's.

 

They are are S4 cuz the nameplate is on the top... So this was ported by atkins, I'm sure the rest of the engine was ported by them too then. Saves me money. LOL I didn't know anything about the stamps. Thanks for the reply on identifying the S4 or S5 parts. So very helpful... Does it matter if I use the S5 f/r irons and what not with other S4 parts or is that a "no no"? Now 4 the missing stud, where do I go to buy a replacement. I dont'e ven know if that is a stud. LOL (second pic)

 

The intake and exhaust both have studs...either pull them out of your old housings with vise grips, or head to lowe's to the metric hardware cabinet and find something that fits. Even if you can only find a bolt in the appropriate thread, you can use a cutoff wheel (die grinder or dremel) to slice off the bolt head and there is your stud. Just thread a nut under the head before cutting it off, so that when you remove the nut, it takes the burrs off the edge for you.