this is the plate in question. tiny ports . What do you think this came out of? No coolant seal grooves.

injector defusers

appear to be injector holes




this is from a 1985 se 13b for comparison

1985 se no injector ports

 

Edit: Ok, this forum is not letting me say RE-SI in all caps so I'm trying it again.

Ok it worked.

What you have there is an RE-SI intermediate plate. Your other plate in NO spec but this NO-spec iron has the same size ports as a GSL-SE and S4 NA and S5 NA.

Thanks for showing us the comparison and using a thrust bearing as a visual aid.

 

So what is a RE-SI? What did it come from , JDM motor? Also the port is very tiny in this , much smaller than the 85 SE port.

 

I know it's tiny. I've had all three in real life. GSL-SE, RE-SI and 6 port 12A.

RE-SI is Rotary Engine Super Injection and came stock in the Luce. It came out like a year before we got the GSL-SE.

It seems Mazda was pretty timid about their 6 port stuff until they got to the FC. The first generation of this new fangled 6 port stuff was the 6 port 12A and those ports were narrow as Hank Hill's.. well you know. Then the RE-SI came out which was the first fuel injected 6 port, and its ports weren't narrow, but just very very short, like Billy Joel Concert (just kidding). Then the GSL-SE had larger NO-spec sized primaries and is a good upgrade for an RE-SI engine. The S4 NA kept the same NO sized primary port size but increased the height of the both sets of ports on the end plates, both downward and upward. Downward on the low RPM ports like all FCs and FDs got on their end plates, and upward on the aux ports giving a slightly later closing timing. The FC did other things to increase power over the GSL-SE too. The GSL-SE was said to have had 135HP while the S4 NA had 146HP. The S5 redid the intake manifold, added a dynamic chamber and some other things and increased HP up to... j9fd3s will fill in the blank.

 

the blank bit is the exhaust, the FC uses 50mm exhaust and the FB is something like 40? larger outlet on the manifold too, its a good upgrade if you need to keep a stock manifold. throttle plates are larger in the FC, as are the ports.

they touched just about everything but for power its all basic stuff, bigger ports, bigger throttle, bigger exhaust..

 

so there are four different center irons for a pre 86 engine with fuel injection,

the USA GSL-SE, N304-10-400,
the Japan Spec 12A Turbo Cosmo, N236-10-400
the 12A Turbo for the Rx7, N253-10-400
and the 13B-SI engine from the Cosmo, N307-10-400

if you look on the oil filler part there is a letter cast in, and that will tell you which one it is. i show the N253 as a K, and i want to say that the N304 is a B?

 

maybe an M. Wish I had a use for it. Now that I washed it off there is almost zero step wear

look at the bigger picture

 

my guess is that it is the RE-Si engine.

we know the GSL-SE letter (well we could if i went and looked), and the port is different, so then;

the RE-Si engine, we know has teeny ports like that, so this is possible.

the other choice is a 12A-T housing, there were two, one is a K, probably the Rx7, the other is unconfirmed