So I hate to revive this again but I'm looking at some rotors here. They have cast compression divots but have 12 roll pins around the stat gear. I thought only S4 rotors had 9 and only S5+ had 12. How do I know if they are NA vs turbo?

s4 rotors have all the fixing pins, but is still cast surface in the bath

s4 turbo ones often have a visible "I" strike dimple in the bath ( clean off the carbon )
and the bath is fractionally wider than the NA one
ie. measure the straight section at the top of the bathtub, not including the curved shoulders

the turbo rotors are about 30 mm along the top ( or inside well ) of the bath
and the NA one is about 25 mm

Thanks bumpstart. What I originally thought were some S5 rotors turned out to be S4 TII

for a turbo buildup.. s4T rotors are preferred by many .. they are stronger under boost

s5 rotors where lightened by thinning out and moving the supporting ribs under the rotor surface

mild detonation , while often not enough to break aftermarket seals
often dents the s5 and FD rotors between the bath and the rotor tips

That's interesting to know. My S5 franken-motor has a REW rotating assy inside so I'll keep that in mind when I gp to boost it. Also want to run on propane but that's a different convo for a diff day unless you want to pm me.

there are a couple of JDM shops that mill the S4 rotors down to 8.3:1 for high hp turbo builds.

My rotors might just be NA.

Rotors are indeed 9.4:1.
Irons sold but everything else available! Come and get it! I have a UIM and exten mani also!

I have some Frankenstein rotor housings.

They are definately S5 NA housings but they do not have the spot for the knock sensor but the plug holes are in the correct S5 location.

Euro or jdm possibly?

Not sure, but a good question.

I stopped by the shop where my engine was being overhauled and they showed me the new rotor housings they where going to use. I wanted to see what the difference was between the spark plug location for my own curiosity, so I put my old housing right up next to the new one and sure as shit the holes where in the exact same locations.

They say "hiroshima blah blah" on the top whereas my old ones don't say anything.

Well i would think the "hiroshima" wouldn't mean jack cause they were built at the Hiroshima plant IIRC

Perhaps in the same context is is strange that the ones he already has don't have those castings on them.

For example, last year I sold a set of rotor housings which instead if just a Mazda logo cast in the plug side, they said Mazda Aviation Division, and they did not have the Hiroshima castings. I had never seen anything like it before.

maybe they are S4 turbo housings...

https://www.rx7club.com/2nd-generati...-s4-t2-816116/

Bumpstart posted lots of info in this thread and if I am reading correctly, S4 Turbo housings have the S5/S6 spark plug locations but still lack the knock sensor casting. Too bad the pics no longer work.

EDIT: i read a little bit further and there are oddball S5 NA housings without the knock sensor hole and some oddball housings for the S4 turbo that have the S5 spark plug holes.

mazda aviation division i suspect means they where made for mistral engines/ beech aircraft for airborne 13b or 20b's
kinda surprised you lot havent twigged, and made a run on the avail mistral thick 20b centreplates and cranks

next .. get your head around the fact that the US is the exception to the rule

( i know that may be hard for those that think the USA is center of the known universe.. but once you do that leap of faith .. , then housing design sequence becomes rather easy to follow )


the s4 turbo housing in all other countries except the US
has same locations for leading plug as s5T ( and s5 NA ) housings
but there is no spot for the knock sensor
usually there is hiroshima patent writing in bossed font on top of housing
.. later replacement housings built to this spec will lack this font
these are known as n318 housings indeed this number is cast into them near the oil injector hole

your US s4T housing with the odd location is known as n332 ..
\because you are the odd man out.. you are actually the minor market
.. i would expect that availability of n332 housing batches at times dwindles
while they can order an n318 housing..
or an n370 housing
( both the same, but that knock sensor hole )

or an n350 housing ( s5 NA )
( same again, but the exhaust waffle insert and blind water crossover and the knock sensor hole )


.at any moment ...

it is a relatively simple matter to blind or unblind the water crossover hole and swap the exhaust port inserts and make all three of these housings essentially interchangeable
( as you only need one threaded knock sensor hole )




in all these countries except the US

ONLY the n326 housing ( s4 NA ) has that odd leading spark location which is closer to the centreline

n326 looks just like n318
( except spark location , the blind water crossover hole and the waffle type exhaust port insert )
and has the hiroshima patent writing on top..
( again.. later s4 and new batch units will not have the hiroshima patent font )
but n326 lacks the n318 ( or any ) bossed marking ( ie.. has nothing there at all )


from the pics below...... all of these housings,, with the exception of the far left housing are actually 6p NA housings

the far left housing is the n318 housing ,, you can see n318 bossed on one of the pics near the oil injector,, and can see the hiroshima patent font

the three housings from the right, are n326 clearly have the higher ( odd ) leading plug location
none of them have knock sensor holes,, all are blind in the water crossover
( two have the exhaust port dropped out ( on purpose for worked use )
,, one ( the gold one ) retains the waffle as original

only one ( the gold coloured one ) is old enough to have the hiroshima font

the two s5 housings are n350 .. they already have the exhaust ports worked, and swapped for turbo inserts
the give away however ( knowing both came from the same engine )
is that we have an F and a R stamp from factory on top.. and both holes for the water crossover are blind
( in a turbo engine,, both housings would have had turbo exhaust inserts and the rear one will have an open water crossover to the inlet manifold )

the far left housing is pure n318 ( marked at oil injector ) and for all respects resembles s5 turbo housings except no knock sensor hole

turbo inserts .. hiroshima font . lack of knock sensor holes , lower leading plug location

what is to bet you can read n318 next to the oil injector??

Engine is fully assembled so i cant see it, but it is EXACTLY how you describe. So I guess I have N318 housings.

we make a lot of noise, but at the end of the day there just isn't any real demand for the 3 rotor stuff

since someone linked this thread i wanted to make a note:

most all rotors have an "I", that doesn't mean they are turbo. turbo rotors have a "T" and an "I" or "II" for engine placement. 20B engines usually are built with all rear "II" rotors.

sorry to revive the thread but I'm trying to figure my parts out. I have what I believe to be s5 irons. Rotor housings and rotors were s5 t2. My rear housing has one bolt for the clutch inspection plate/cover but it doesn't have the reinforcement on the oil pedalstal. ???

is it s4? S5?
https://cimg0.ibsrv.net/gimg/www.rx7...71976a9f6.jpeg

https://cimg9.ibsrv.net/gimg/www.rx7...da4a60800.jpeg

casting letter will tell you. temp sensor thread too.

N370-10-C50 is for cars before 10/89

N370-10-C50A is 10/89+ presumably the difference is the thicker casting

all that Mazda sells is the A with the big casting

that's too many numbers :/ all I have stamped on the rear iron is a "D"



https://cimg4.ibsrv.net/gimg/www.rx7...fe42202fbd.jpg


https://cimg0.ibsrv.net/gimg/www.rx7...7aa4f47b9b.jpg
I dont think this "I" means anything


https://cimg1.ibsrv.net/gimg/www.rx7...40a17b5b70.jpg
"B" ?

Ya man this is what I'm talking about. I only have the one bolt hole on the top of the iron. Only reason why I question this iron is because I don't have that extra "bridge" for reinforcement or a thicker casting like the one that is currently in my car.

Everything else points to be s5 except for the rear iron because of the non existing reinforcent bridge thing.

Did I end up with defect? Did all s5 engines have that reinforcent bridge then later added a thicker casting to that bridge? Or is this a weird s4 plate with one clutch inspection plate for whatever reason? An early s5? Meaning 10/88 perhaps ... ??

the D casting letter is an S5, there are TWO S5 irons, the early one, with no reinforcement and the later one with the reinforcement. you have the early one.

Thanks man, I appreciate you 👍