13b rotors in a 12a
 

hi guys, yes i tried to search already, i just got a 13b for 200 bucks that has bad housing seals and leaks coolant, i was just wondering what is needed to be changed over from the 13b besides just the rotors into the 12a i am at the point of pulling my 12a and i was just going to rebuild it with a port job, but was thinking about putting the 13b rotors in it. Would it be better if i put the 13b rotors in it? or just keep the 12a rotors in it? any opinions would be great. I have not yet decided what i want to do. here is the 13 be i took apart, rotors look like they are in good shape but the bearings are bad, they are very scored and are very unsmooth. also its an 87 N/A 13b

You use the irons from a 12a and the housing and rotateing assembly to for a 13b 4 port.

I do not believe that you use the 13b rotors with the 12a housing just because of the width of the rotors.

Can't do it. The coolant seal grooves were moved from the housings to the irons in 86 and the 13B rotors and housings are wider than the 12As. If both engines were pre-86, then you could use the 13B rotors, housings and e-shaft to build a 13B 4-port. As it stands now, you build a 12A or an FC-S4 13B and you can't mix and match them.

this is where you choose, mi lad ... 12A or 13B. you can't have both.

damn that sucks huh, im going to keep both engines but i dont know which one i want, im probably gonna go with the 12a,damn i really wanted to do that 13b with 12a, o well i guess ill just port the 12a, thanks you guys for the help, ill keep you guys updated on the project, just gotta take more pics, ill probably have the 12a out today:) i cant wait to see how it is, the 13b was nice, it had some minor damage but o well.

use the irons from the 12a w/ 13b housings and rotors the port on the 1a center iron is better!!

but i thought trochoid said i couldnt do that?? im confused:)

It would work as long as you had rotor housings that are pre 86, which have the coolant seal groove in the housing and not the irons, and then you'll need to use the 13b rotors, e-shaft ect. because the 13b rotors are wider than the 12a.

Only way you can do that is if you use an 84-85 -SE 13b irons or any other pre 85 13b. I have a -SE in my garage with half bridged 12a irons I plan on throwing together, whenever I can gather the moo-lah for another housing/rotor (pretty scarred up)

What is so great about teh 12A housings?

They're narrower than 13b's.

I built a 4 port 13B today using 12A side plates and '74-'75 13B rotor housings and shaft. I used the 12A thrust assembly because the early type were notorious for failing (I know of several early engines with failed thrust bearings and washers, but few later ones). Mine was actually in the process of self destructing. Glad I caught it in time. :) I also swapped in some '76+ stationary gears because they're stronger (gear teeth are longer adding strength).

cool, i dont know, i think i might just build both motors seperatly but its a lot of money for a rebuild kit.

You may have thought, but you didn't read with comprehension, Reread what I posted and think about it. What I stated is true and workable.

RX7 and money go hand in hand. :)

yeah,lol o well i have a long time to restore this baby, an im gonna take my time. Thanks guys.

Hey guys I'm confused again. (not that hard to do :-)
I have an 05/85 - do I have a 12a or 13b? If it's a 12a, & I find a 13b for parts, what's the advantage of using the 12a housings? What is a "4-port" & what is the, umm, alternative?
Thanks,
~ Paul
aka "Tha Driver"

There is no problem that cannot be solved with the *right application* of high explosives.

You could have either, is your car a gsl-se or other, only the gsl-se has a 13b, for fb's anyways. easiest way to check go to your car and look at the top drivers side of the rotor housings it will either have 12A or 13B cast into them.

Thanks,
Mine is a 12a. So I should look for a 13b for rotors & other parts? Again what is the advantage of using them with the 12a housings; what is a 4-port, & what is the alternative? :-)
~ Paul
aka "Tha Driver"

I'm not a complete idiot, some parts are missing.

In general, for the most part, 12a and 13b innards are not swappable. This is a generalization but the rotors, rotor housings and e-shaft are wider/longer so they can't be used, counterweights aren't the same so they can't be used, and irons can't *always* be used because of placement of the water seal o-rings depending on the year of the engines involved.

12a engines have a "4 port" design, which means that there are two intake ports/runners per rotor, for a total of four. Later 13b engines had a "6 port" design, where there are three ports/runners per rotor, with one of them activated/actuated by an exhaust-pressure-driven valve/flap setup.

The 4ports are easier to "port" (enlarge the port size of). The 6ports are better for gas mileage, and when talking in stock terms, allow you to keep the low end torque while still having some top end.

To keep things simple, since 4port irons are better for porting anyway, just stick with 12a parts. There are a few aftermarket things like hardened stationary gears that you can get if you rebuild, to help make the engine stronger and more reliable.

Jon

OK but... this thread is all about using the 13b rotors & housings on 12a irons etc. etc.
Is that not a good idea? If the 13b rotors are wider wouldn't that give you more displacement? If I ported the 4-port irons would that give me more HP (over the 6-port 13b irons)?
Just looking to get more power on a budget. If I had lots of $$$ I would just build a turbo three-rotor. :-D
It's all speculation at this time anyway 'cause I have other projects ahead of my RX7, but I *would* love to get it running & drivable - & I'm *not* going to build up a stock 12a.
Thanks,
~ Paul
aka "Tha Driver"

Headline: APATHY RUNS RAMPANT - Nobody cares.

To put things in a simpler perspective, and the thread tittle is vey misleading, it should read something like, 'Using 12A irons on a 6-port 13B SE engine'.

Can it be done, the answer is yes. Why should it be done, better porting can be performed on the 12A end irons than on the 13B ones and it will yield more hp. Using the 12A center iron yields more air flow also. Only restriction is the 13B needs to be 85 or older. Then find the appropriate intake manifold. That may be frustrating.

OK thanks again.
That's great: I'll keep a lookout for an early 13b to do that with. I can make my own intake & exhaust; in fact prefer to do so in order to run whatever apprpriate carbs I come up with.
~ Paul
aka "Tha Driver"

If guns cause crime, all of mine are defective.

Don't forget that there is no provision for injectors on the 12a irons, so you'll have to modify the lower intake manifold to put the injectors in it... or convert to a carb setup.

Jon