Hi guys,
Im new to rotaries and still learning.

From what ive gathered i think i have a na 4 port rx4/5 cosmo engine or a bitsa?

It has large italic Mazda in a box frame, front and inter irons have letter 2 stamped and on rear side of rear iron has the letter N.

Is it standard port size?

Rotors baths are cast iron they have 3mm apex and 1mm side seal grooves so guessing they would be a early gen wouldnt they?

so the pics are linked any help is greatly appreciated, still learning so take it easy on me haha.
If any specific pics are needed let me know.
thanks, Joel

http://s1242.photobucket.com/albums/gg522/rotaryute86/

 

Looks like an RX-4 13B. Someone has ported the exhaust.

 

yes it's a pre-79 4 port 13b. mine is from 74 rx4, alto mine had the sensor in the top of the center iron but made a plate in it's place. urs doesn't have that so i'm guessing 76 maybe? urs might actually be from a repu.

 

13b rx4?

 

So it's a early 4port 13b. Are they they the original irons or are they 12a irons , was told they might be.

 

yes. the rx4, cosmo(rx5 to some areas), and rotary pickup(repu) had a carbed 4 port 13b in them.

 

Looks like 12a tall center port iron,unless rx4 had those which I doubt.

 

Sorry, but what is the difference between the 2 ? In terms of my knowledge, I thought it is one kind of iron.

 

Do the tall ports respond better to porting or is it pretty much the same?, and is it only the centre iron that's from a 12a?

 

The tall port iron gives you more room to port. Generally when people port the small port irons, they bring them out to tall port specs or just a little beyond. But you quickly run out of material.

That's a good point on the 12A end irons. The runners look 12Aish. 13B runners are taller.

 

Ok so it could be 12a irons with rx4/5 housings. Did the repu engine have the centre tall ports?

 

The REPU and Cosmo RX-5 both had tall port irons.

 

How do I tell the difference between the 12a,Cosmo,repu irons

 

Compare picture of all of them.

12A irons have much smaller intake runners which are more roundish, as well as smaller ports.

13B irons from a Cosmo/Repu have taller intake runners and larger ports.

 

thats a 13B from and early Rotary like Rx4/Repu Truck

 

I'm finding it hard to compare the difference between the 12a irons and the Cosmo/repu can anyone give me some ideas on Wat I should be looking for like the difference in port sizes,runners what lettering is cast onto the each specific iron?

If anyone could post pictures of the plates (12a and cosmo,repu) and explain the differences that would be greatly appreciated

 

Or even just a good thread explaining the difference with pictures to compare my irons to would be good

 

I'd post pictures, I just don't have all of those irons to take pictures of.