i was on rx7.com and i came across an article that hints to using 13b rotors in a 12a engine. does any one know if this is possible?

 

w/ 13b housings and internals, but for all intensive purpose its now a 13b w/ 12a irons

 

It's now refeered to as a 13b 4 port motor. And yes it is done all the time.

 

To clarify what has been said, you can use the irons from a 12A, and the rotor housings, rotors and e-shaft of a 13B to build a 4 port 13B.
13B rotors and housings are 80mm wide, while the 12A rotors and housing are 70mm. As you can see, there is a 10mm difference, so the rotors cannot be used by themselves.

 

what kinda power gains would you get outa this swap cus i have a 13b block and the 12a in my fb would it be worth my time and money to do this with a streetport instead of a regular rebuild and a streetport

 

very interesting Im tuned in.

 

yes do the swap. You'll find it easier to find parts for your new 13b down the road then your 12a in a few years. You should join up on www.bcrotary.com its our local site. My name over there is Super7 and i'm a moderator. Its a good local site with quite a few knowledgeable people.

 

The power can be anywhere from ~130-140HP and up. It depends on how the engine is ported, and what intake/carb setup, or FI system, and exhaust is used in conjuction with the 13B.
The hardest part, is the 13B rotor housings must be from an 85 or older 13B. The 86 and newer housings can't be used with the 12A irons.

 

is there like a like general guide for doing that build?

 

Basic guidelines are:
Good 12A irons.
Good pre-86 13B rotor housings
Good matching rotors and counterweights/flywheel from any 13B, 89-91 N/A rotors are usually preffered, higher compression ratio, unless planning a turbo later.
Good e-shaft from any 13B, but pre-86 is usually preffered, due to no "Thermal pellet"
Beyond those parts, you will also need an intake for whatever type of induction you desire, and the exhaust manifold for turbo or header, a full rebuild kit, plus a few other odds and ends needed to complete the build.
Since you will have the engine apart, might as well choose what type of porting will suit your specific goals and HP needs.

 

Using 12A irons on a 13B is basically building an old school 74-78 13B. With the right carb and a good sized streetport, you will be looking at 175+ fwhp with the proper supporting mods. A full bridgeport can put you in the 225-250 range. It's actually easier to get more hp out of a carbed 4-port 13B than it is any NA 6-port. While you may not have the lowend torque that a 6-port has, the topend of a 4-port is so much more fun.

Assembling such an engine is the same as any other 4-port, no special instructions needed.

 

and by irons i assume you mean apex seals corner seal etc??

 

iron means the big blocks on the ends and in between the rotor housings.

 

Nope, those are seals and springs. Irons are the cast iron parts of the engine, the 2 end plates and the center section.

 

what about the wire harness will i need a 13b harness, and the tranny will i need a new one of thes too, or can i get away with using the 12a transmission

 

Okay wait... he's talking about taking the rotors from his 13b and putting them in his 12a. It seems to me like everything has been turned around the other way. Maybe my headache has taken place of reading comprehension between my ears.

 

Wire harness is only needed if you are installing a later model fuel injected engine, as a complete unit.
The 12A trans is the same basic trans used in the non-turbo 13B powered 2nd gen. They can handle 200HP pretty easily, unless severely abused. Under severe abuse, even a 12A that is mostly stock can destroy a trans.
Only trans upgrade option, that will fit somewhat easily, is a turbo trans. They're not cheap, and require a lot additional parts to make them fit. This has been covered several times, and info about this swap can be found in the archives.

 

Irons are also refered to as side plates.

 

thanks for all the help guys. honestly you just saved me about 500 bucks.

 

We accept donations.....

 

so If I got a 12a on my bench and am looking at a gsl-se to possibly buy just for engine. and or anything anyone else wants, could this be done or would it be easier to re-build it using all the se parts? Therefore I am asking what are the benefits?

Thx matt

 

Depends on several factors. Are you going carb or FI? You can use the 12A irons and go carb. With porting, you will achieve more hp than porting the FI SE or porting a 12A. You will need the SE rotating parts, along with the oil pan. You can use the 12A front cover since the carbs have only 2 mop inlets. If you want to use the SE front cover and mop with it's 4 mop lines, you will need to use the SE center iron for 2 of the ports and buy the injector plug kit. Another option is using the 12A mop and the SE center iron for only 2 mop lines with none going to the carb.

Then all you need is a 13B 4-port intake and a 2 barrel after market carb, 48 mm prefered, or the Holley 600 from RB if you like playing with those.

 

Wrongo.

trochoid, remember all those pictures of side plates and rotor housings we posted a few months ago?

SE and later have oil injector holes in the rotor housings, as do some non-US spec 12A rotor housings from that era.

Also stay away from the SE center iron if you want to run a carb. The tiny ports don't let you port it much before hitting water.

 

You could also get the grooves cut in 86+ housings to mimick SE housings.

 

Goint to need some proof on that.