rotaryute

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/

Aaron Cake

iTrader: (1)

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

rxtasy3

iTrader: (2)

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.

FRSHMN

13b rx4?

rotaryute

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

rxtasy3

iTrader: (2)

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

turbo_dave

iTrader: (50)

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

RX7andI

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

rotaryute

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?

Aaron Cake

iTrader: (1)

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.

rotaryute

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

Aaron Cake

iTrader: (1)

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

rotaryute

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

Aaron Cake

iTrader: (1)

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.

RxManny

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

rotaryute

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

rotaryute

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

Aaron Cake

iTrader: (1)

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