What's the difference between stock USDM 12a side housings and JDM 12a sides? I've found what I believe to be a good deal on a set of JDM 12a sides, but I don't know what the difference is between the two. I'm planning on an agressive street port for them, so if the difference is in the ports and timing then it really shouldn't matter to me which I purchase-as long as the JDM pieces are just as portable as the USDM sides and will mate to an '84 or '85 GSL-SE's 13b rotor housings. If anybody knows the difference or has any info that pertains to the subject, I'd really appreciate it. Thanks to all who reply for your time, help, and information...

-Adam Collins

 

the old JDM 12A irons had penut sise ports where the US one were huge...

RX oe anyone else Send me your E-mail address and I will send you over some photos so you can see for yo0urt self...

Dan

 

That doesn't sound like such a good idea anymore now then. rxforspeed@yahoo.com is my email-I'd love to see those pics! Dan-what would you recommend-porting US sides or JDM pieces? Thanks...

 

xlr8planet@hotmail.com

I took pics of my euro 12a irons

will post them later

 

R5? Y?

 

Here ya go:

http://taylorrotorsports.com/projects/Gary/

The irons are different, but the intake is a 6-port which is where the power difference is. Somebody told me the JDM parts made 5 or so more HP in stock configuration. I've got everything but the housings if you're looking for some.

 

Those primary ports are small, but appear to have the same degree of opening/closing as the USDM ones.

 

I believe you got it wrong trochoid. They open far later but close at US-spec.

 

Thanks Chris-I see exactly what I needed to know now. I didn't realize the JDM pieces were 6-port and would require a new manifold and additional equipment. I need the US 12a irons to build my 4-port 13b then. Does anybody know the best model side housings/irons to use for porting? I've seen a few pics of some irons that don't really look very portable. I don't plan on going huge with the port work, just a slightly agressive street port. I'd like to get side housings that could be opened up a bit more than what I need for when I get hungry for more power on down the road...

Thanks guys!

-Adam Collins

 

Barely any 12A's were 6-port...its a relatively rare motor, and was availiable only in japan. for the most part the majority of 12A's were 4 ports. from what ive read the best housings to use for porting are the "R5" castings from early Rx-7s and prior. the more common/availiable "Y" castings from the later 1st gens can still get the job done, unless you plan on doing some monstrous porting (this is just stuff ive picked up from several years of cruising the forum)

this page may also help a little (http://home.iprimus.com.au/bluey3/portsPage/ports.htm) , but its based on austrailian 12A's and doesnt talk bout the "Y" housings us yankees recieved

 

I've ported Y, nitrided R5, and non nitrieded R5 and it appears the Y and nitrieded R5 are easiest to port. The early non nitrided iron is harder all the way through.

As for room to port, I think R5 and Y have the same amount of iron and water jacket. I've seen some large street ports in both and they appear to have similar castings on the inside.

 

Why do I keep looking at openin/closing from top to bottom and not side to side? Maybe it's the old piston influences.

 

Just think of a bridgeport, and how much sooner it opens than a stock port.

 

Yep, and I even have an acrylic template to lay over a rotor and housing to check that, lol.

 

Where do you find the casting #'s on the irons? I'm sorry Jeff-I didn't realize what you were referring to in your first post in this thread. Where will I find the "R5" or "Y" on the plates? Are the #'s visible without tearing down the engine? I've got a (poorly) running 12a, but I'd tear it down for the irons if I've got the right parts. I believe the 12a is either an '84 or '85 model, but it's in an '83 body. So it's probably got the "Y" irons, huh? Thanks for all your help guys!

 

Yeah, Y probably.

1) look behind waterpump on front plate
2) look either near bottom of oil filler tube or front side down near spark plugs
3) between stationary gear and upper tension bolts

 

I'm home for a little over 24hrs now, so I'll have to check and see what I have. It sounds like either the "R5" or "Y" would work for me if I decided to go the 4-port path. I'm just hungry for knowledge right now so knowing where to look for the casting #'s is all the info I need for now. I've been pointed in another direction that'll be quicker and cheaper to achieve the power level I'm looking for so I may stick with a 6-port configuration if all checks out alright with the engine in my garage. Thanks again for all the info and help guys...

-Adam Collins