When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
So I have been pricing out a build for my 12A my goal is a high RPM, NA motor say 9k bursts. Please tell me if I missed something or if I should think about a certain mod. TELL ME WHAT YA THINK
Questions:
First I have read a lot about apex seals and from what I can tell the best for my application would be carbon seals. They can handle the RPM and I do not plan on running boost. BUT WHERE THE HELL CAN I FIND ANY????? I can't find anyone who sells or still makes carbon seals. Maybe I missed something but if they are not available what other seals should I look for?
Will the OEM side and corner seals be ok for my application?
What modes for the oil pressure should I do?
Any ignition mods?
Should I think about stronger studs for the engine?
Build:
Carb/Fuel
Plans are to run a Weber 48IDA downdraft carb, I am going to be deleting the OMP
I plan on just using the stock fuel pump and lines (Is that a problem?)
Motor internals
Pineapple Racing Bridgeport template along with there recommend exhaust port template
Akins rotary hardened stationary gears with the 3 window main bearings that come preinstalled
Mazda race rotor bearings
The Akins rotary master rebuild kit with the OEM 2 piece corner seals and the OEM side seals
Carbon apex seals (If I can find any)
Exhaust
Racing beat full exhaust system (I am planning on welding an o2 bung)
Trans/Clutch
Racing beat aluminum flywheel with the auto trans counterweight
Not sure what clutch
the Carbon Seal, 4352-11-301 for the 12A and 4801-11-301 are NLA . i think there are better options these days.
the stock fuel lines are ok, but the pump should be tested. i like the stock pump, but you need to make sure its delivering fuel. after that i like the mallory pump, it has a pressure regulator in it.
i know the carter pump is popular, but it doesn't really flow much fuel and the holley regulator kills flow too
you should also get the FD oil pressure regulator, same pressure as the competition part, but its way cheaper, N3A1-14-230
for the clutch, you want something with an organic sprung hub, and ideally a marcell spring, you want to do what you can to keep the trans happy. with a BP you're not really making more torque, you're making it for more rpm, so the clutch doesn't need to be anything crazy
Thanks for the response! I found foxed.ca before but I somehow missed that manual that's a big help.
Are the OEM corner and side seals ok for this build?
I would not run a 12A past 8k or so, or any other engine with 9 pin rotor gears.
There are band aid fixes like hardened stationary gears ($$$) and circlipping the rotor gears into the rotors to keep them in place, BUT....
Good 12A parts are extremely hard to find. 12A rotor housings are pretty much nonexistent, although for something like $2500 you can get 13B rotor housings cut down to 12A size. Next problem is rotors, which are even harder to find than rotor housings. I have seen 12A rotors trashed past any usability in as little as 30k miles. Goopy make oversize 12A apex seals but they are only .003" thicker, they would need to be .030" thicker for most 12A rotors I have seen!
If your trying to build the ultimate na engine why not make a 4port 13b. U can still use the 12a irons from your old 12a. 13b gslse rotor housings are still available new. Except for gslse the 13b rotors and eshaft are a lot lighter than 12a. Make a rev happy motor that will spin freely. If u got the coin try to find s5 na rotors and eshaft. A matched set so you don't have to get everything balanced. If u got the money to spend u can still get 13b carbon Apex seals from mazdatrix. Last time I looked they cost $1500+ -
per rotor.
I have run Carbon seals, Mazda seals and Adkins seals in various engines. In the stock port 12A with OE Mazda seals had a noticeable torque increase over Carbon seals in the same engine. I have no A to B comparison with the Atkins seals, but they seem to be fine in my GSL/SE 13B Street Port engine.
It would seem to me that a bucks up, no holds barred NA engine would use Ceramic seals
"If your trying to build the ultimate na engine why not make a 4port 13b. U can still use the 12a irons from your old 12a. 13b gslse rotor housings are still available new. Except for gslse the 13b rotors and eshaft are a lot lighter than 12a. Make a rev happy motor that will spin freely. If u got the coin try to find s5 na rotors and eshaft."
Unfortunately I do not have an unlimited budget lol but that is a good point finding parts would be much easier for a 13b build. Does the 13b gsle housing fit the 12a subframe in an fb?
At this point I should think about a PP on a 4port 13b . As I stated before I don't have an unlimited budget. The point of this build was its a little cheaper than a PP but maybe if I'm going to spend this much money I should just go all out.
If you do not have an unlimited budget, do not build a 12A! Those are incredibly expensive to build anymore. Parts simply do not exist and when you find anything for sale it will be garbage, expensive, or both!
I bought many, many engines a few years ago trying to build a stocker, including a "rebuilt" engine for $1500. All that I got out of that engine that was any good was another eccentric shaft. Rotor housings were junk, side housings were junk, apex seal slots in the rotors were so worn you could stick a side seal in there next to the apex seal, and the best part is that it had one light and one heavy rotor in it. I literally have a wall of shelves full of junk 12A parts that I drove halfway around the country scouring up to find over a period of a few years.
Your easiest bet for aformentioned 4 port 13B is to get a junk 12A for a few hundred, send its side housings to Chips to be resurfaced because in 2022 they will probably have rust damage. A set of new GSL-SE rotor housings for about $1100-1200, a FC N/A core engine for its rotating assembly.
Yes I did just describe a $4000 engine.... and this will be cheaper than trying to piece together enough good 12A parts to build an engine.
I still think it is kind of a bad idea to do it because 12A bits are hard to find and you may open up your engine and find out that it is not in the best shape with respect to chrome flaking and rotor wear.
You CAN have a lot of fun keeping it under 8k. I went for a couple years with a bridge ported GSL-SE engine, it wasn't the best because 6 ports suck (made 135whp) but it made plenty of midrange and it lasted well enough keeping the revs low.
I used to have a peripheral port 12A with all OE internals, too. Carbureted and fuel injected. Fuel injection is 1000% the way to go if you care about drivability. That one made about 160 at the crank going by injector duty cycle.
The next hard part is finding decent manifolds for it. 12A manifolds are difficult to find anymore. The wraparound manifolds are not very good, your best bet is an Atkins manifold setup.
My 4 port 13B made 208whp on a Mustang dyno, was making 200 crank horsepower at 6000rpm. 13Bs are more thermally efficient and the later ,7mm side seals and 2mm apex seals are way more efficient with respect to friction, and staying in contact with the rotor housing without flapping around, which kills the chrome and the apex slots. That is why it is far easier to find FC engines with good rotors and good rotor housings.
you should price both options out, even in the 90's when you could get 12A parts it was only $50 cheaper to built a 12A
the recipe is something like 12A irons, GSL-SE rotor housings (ideally new), and then the rotors, eshaft tension bolts and stat gears from an FC engine. (or FD if you buy some new S5 NA rotors)
All u need to drop a 13b in a first gen is a racing beat motor mount and gslse oil pan. With the price of parts it's hard to do a "budget build" now days. Even back in the day 1997 when I rebuilt my first rotary engine it was expensive. So save your money and do it right. With a mild street port from racing beat on a 4 port motor u can make really good power. 12a irons are easy to port yourself. They have lots of "meat" so you don't have to worry about cutting into the coolant side like the later engines. I searched far and wide for a matching s5 na rotating assembly that was good for my ultimate na build. I've built a few with s4 rotors and u can't tell the difference really. Very minor differences between the two. U can find s4 na stuff pretty much anywhere. Fairly cheap. My original 4 port i built is still going strong going on 5yrs I think. I started with a mikuni phh44 and now gone crazy money EFI set up. Ida throttle body standalone ecu. Made 192hp on a hub Dyno shitty tune. EFI is by far the way to go on rotary's. Can be done fairly cheap with a sniper. Installed one on a 4port 13b with s4 rotors and that car with Miata trans is fast not as fast as mine but plenty fast. It doesn't take big horse power to make these little cars go. Just the right combo of parts.
.
you should price both options out, even in the 90's when you could get 12A parts it was only $50 cheaper to built a 12A
the recipe is something like 12A irons, GSL-SE rotor housings (ideally new), and then the rotors, eshaft tension bolts and stat gears from an FC engine. (or FD if you buy some new S5 NA rotors)
when u build a 4 port with 12a irons u need to use 12a or gslse 13b stationary gears. Or have the s4 or s5 gears machined down. That's what I did with some turbo stationary gears. The gear is too tall. When you put it all together the engine will be too tight. Won't spin. Found that out the hard way.
All 13B stat gears are the same dimensions, any 13B use any 13B stat gears, 12A need 12A stat gears. The only gotcha is FD front gears are different for some reason I can't remember (bigger thrust bearing?) and RX-8 rear gears have no O ring groove so you have to use a little silicone.
I run up to 10k and a little beyond with boring stock GSL-SE stat gears, because that is what I had lying around.... the key is the 12 pin rotor gears (anything '86-up).
Lots of good info thanks guys! I thought to get an 13b into a fb u had to swap the subframe witch actually is a pretty good upgrade suspension wise. I like the carboration though I think its cooler. I kind of forget does the "s" mean generation?
The GSL-SE had a different crossmember but the geometry is the same, it just has the motor mounts shifted 20mm forward. Racing Beat sells an adaptor mount bracket to put a 13B on a 12A subframe, or you can bend a 12A bracket to work. I have only ever used bent 12A brackets but somehow I have a brand new in box Racing Beat adaptor bracket on the shelf, along with a brand new in box GSL-SE oil pan (the other part you need). Using a bent bracket seems more real to me, somehow
Thanks Peejay I think you guys have changed my mind. I think now I will full bridgeport this 12a for the hell of it and only replace parts it needs. Then ill build a 13b and eventually swap it in. I want to carborate the 13b though.
08-10-22, 05:19 PM
12A Full bridge Build critique and questions
