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It is a six port 12a jspec. Mazmart and NYBE sold tons of them back in the day. Some had the six port induction sticker, some didnt... I bought 1 or 2 of them and ran them.... they ran good
it is a six port 12a jspec. Mazmart and nybe sold tons of them back in the day. Some had the six port induction sticker, some didnt... I bought 1 or 2 of them and ran them.... They ran good
Yes Dave it came in exactly as described by the ebay ad and photos, see the picture immediately above for the cleaned up unit and there are some additional photos on the previous page.
I sure would like to see a photo of one of these things installed in one of the cars they came in!
I have one of the carbs and engines they came on, Ray. 6 port 12A. Odd duck is what it is.
I spent time doing my typical carb mod work on it yesterday, but the carb is very strange and may not take kindly to my reprogramming to handle boost. Not that I'd do that on this carb anyway.
Well, it is a factory 6 port 12A Nikki and I have the matching factory intake manifold but don't have the cool black air cleaner assembly.
The engine it came on was a real 6 port 12A, complete with microscopic pee shooter primary port runners and really narrow ports. Super late port opening in other words, but similar 12A spec closing timing. The end plates were simialr with ports smaller than a typical GSL-SE. The goal is to swap in a Y intermediate plate and GSL-SE end plates for much more total port area and no porting required. Sadly the intake manifold's pee shooter runners are my main restriction here, so I'm going to max them out on the Y and -SE irons.
As for the Nikki, it is getting all of my knowledge thrown at it. The primary circuit is hogged out and boost prepped the same way I do all of my carbs that have proven to handle NA and boost perfectly . The secondaries are where the twilight zone is. The original secondary fuel jets in this carb were only 120, compared to a stock 4 port Nikki which has 160. However this odd carb also has another hole drilled into the long slow bleed circuit, at about the 160 size, from each float bowl into the long slow circuit. The long slows are of a different configuration as well, which I assume was to take advantage of the additional fuel. This extra fuel becomes available only when the aux ports open. The carb is carefully calibrated from the factory for all of this and is why I'm scratching my head for how to go about hot rodding it. The stock main air bleeds are also calibrated differently than a 4 port Nikki. I deleted the primary air bleeds at 90 and went for some adjustable ones with a drilled 70 pilot jet and moved the factory secondary 120 fuel jets to the primary side, as they are drilled to about 117 to 118 metric, and are perfect for the hogged out primary venturis I installed. I then swapped in a set of metric 121 jets in the secondary side for now, to deal with the increased air flow through the GSL-SE end plates. Of course wideband tuning will be required to get the carb just right but this tune is a good place to start.
Another odd thing about this carb was the factory vacuum secondary box and lever arm. It had a different amount of leverage required to make it work. Seeing as the factory primary venturis were only 18mm, not your typical 20mm found in all 4 port Nikkis, something told me the stronger or possibly weaker? vacuum signal produces a different amount of vacuum and required a different amount of leverage... I deleted it and went mech secs as usual.
What I wanted to do is fully boost prep this carb by swapping in some 80 modded secondary air bleeds and solder filled long slows, but due to the weird way this card is set up from the factory, I don't know if I can do that. Fortunately it's all adjustable though, so swapping in the boost prepped parts only takes a few minutes. Then I can test it on my turbo.
Yeah, maybe I'll do that. Then pull them and swap in the 6 port parts and set it aside until the 6 port 12A is built. Thoughts?
I don't have any pics right now. If I think about it today, I'll snap some for you guys.
Well, it is a factory 6 port 12A Nikki and I have the matching factory intake manifold but don't have the cool black air cleaner assembly.
The engine it came on was a real 6 port 12A, complete with microscopic pee shooter primary port runners and really narrow ports. Super late port opening in other words, but similar 12A spec closing timing. The end plates were simialr with ports smaller than a typical GSL-SE. The goal is to swap in a Y intermediate plate and GSL-SE end plates for much more total port area and no porting required. Sadly the intake manifold's pee shooter runners are my main restriction here, so I'm going to max them out on the Y and -SE irons.
As for the Nikki, it is getting all of my knowledge thrown at it. The primary circuit is hogged out and boost prepped the same way I do all of my carbs that have proven to handle NA and boost perfectly . The secondaries are where the twilight zone is. The original secondary fuel jets in this carb were only 120, compared to a stock 4 port Nikki which has 160. However this odd carb also has another hole drilled into the long slow bleed circuit, at about the 160 size, from each float bowl into the long slow circuit. The long slows are of a different configuration as well, which I assume was to take advantage of the additional fuel. This extra fuel becomes available only when the aux ports open. The carb is carefully calibrated from the factory for all of this and is why I'm scratching my head for how to go about hot rodding it. The stock main air bleeds are also calibrated differently than a 4 port Nikki. I deleted the primary air bleeds at 90 and went for some adjustable ones with a drilled 70 pilot jet and moved the factory secondary 120 fuel jets to the primary side, as they are drilled to about 117 to 118 metric, and are perfect for the hogged out primary venturis I installed. I then swapped in a set of metric 121 jets in the secondary side for now, to deal with the increased air flow through the GSL-SE end plates. Of course wideband tuning will be required to get the carb just right but this tune is a good place to start.
Another odd thing about this carb was the factory vacuum secondary box and lever arm. It had a different amount of leverage required to make it work. Seeing as the factory primary venturis were only 18mm, not your typical 20mm found in all 4 port Nikkis, something told me the stronger or possibly weaker? vacuum signal produces a different amount of vacuum and required a different amount of leverage... I deleted it and went mech secs as usual.
What I wanted to do is fully boost prep this carb by swapping in some 80 modded secondary air bleeds and solder filled long slows, but due to the weird way this card is set up from the factory, I don't know if I can do that. Fortunately it's all adjustable though, so swapping in the boost prepped parts only takes a few minutes. Then I can test it on my turbo.
Yeah, maybe I'll do that. Then pull them and swap in the 6 port parts and set it aside until the 6 port 12A is built. Thoughts?
I don't have any pics right now. If I think about it today, I'll snap some for you guys.
You're right about the 6 port making less vac to work the secondaries. They work best mechanically.
Thanks for the details on the 6 port Nikki Jeff, I'm beginning to understand.
I guess to do this kind of work properly you need one foot on the west coast and the other one in Japan, which is hard to do from where I live in rural Georgia.
So for me I guess the closest I'll ever get to 6 ports, 13B or 12A, is my nifty black air intake.
Although I hear the Rotary Gods grumbling that the right thing to do would be to send it to you to be reunited with the proper carb.
That painted one does look remarkably similar! And that green is very cool too.
But I'm scratching my head over that stock exhaust manifold.
That stock exhaust manifold looks strange to me. My 6 port 12A came with a cast iron mini "header" of sorts. Very short and small, but I do believe Mazda calibrated it for the flow of the engine with stock ports. Of course mine will not have stock ports so I'll just use an RB header with it. I'm thinking of trying it with RB's long primary exhaust and maybe seeing if there is a way to wire the aux ports open until I can get the actuators to function.
Ray, the actuators of this vintage used the ACV channel which is prone to filling up with carbon and not working anymore. The later ones like S4 NA still used exhaust backpressure, but they employed a small steel 3/16th (3mm or so) hardline piped into each side of the intake manifold. I think to get my aux ports to open reliably, I could either plumb a set of brass fittings into each side of the manifold and pray that the rubber hose doesn't burn up due to header heat, or maybe graft an FC hardline in (lots of work) or see if the central ACV cover/delete plate from RB could be tapped for a single fitting, up away from the heat, and route a tube from the header up to it.
Like this:
I think this 6 port 12A, with functional aux ports and properly hotrodded, would make an excellent daily driver for someone. Low end torque of a 13B with high end power of a streetported 12A. Best of both worlds.
A picture of someone's 6 port 12A intake manifold I found on the forum. It looks like mine except mine was not bludgeoned by an air powered scuffing tool. Anyway, the runners are so small! The positions are compatible with 13B 6 port end plates as far as I know, with a little kiss here and there. The primaries are at the bottom of a tall Y runner intermediate plate and the void at the top must be filled with quicksteel or similar putty. I can gasket this thing if I buy a GSL-SE gasket and a 79-80 gasket, and cut/blend them together.
Here is the engine I have, before teardown. Notice the strange waterpump meant for the water choke.
EGR port like an S4. Tag says it was pulled in 1994.
Awesome cast iron header. Small (restrictive) but interesting Note the motor mount studs like a GSL-SE.
Genuine 6 port manifold with matching Nikki. Note the long secondary vacuum lever arm peaking out from under the bag. This engine must have had very weak vacuum signals at low RPM. Ugh. Note the cast iron waterpump inlet pipe. Heavy.
'80 type dizzy. Short oil filter pedestal. Motor mount studs. Very grimy.
The 6 port rotor housings have these weird holes in them. Obviously to pipe the 'backpressure' up into the intake manifold and ultimately into the aux port actuators to open under load.
Nice closeup of the holes. Note the large amount of carbon flakes in the port. This engine was carbon locked due to an always closed (non functional) water choke.
Then I realized those holes looked familiar. Here are some pics of a set of genuine 12A turbo rotor housings we used in carbed 4 port 12A a few years ago, back when you could still get new ones.
Note the nice big 12AT spec ports.
Also note the holes down below. These are compatible with the 6 port 12A cast mini header thing to supposedly force backpressure into the ACV channel to open the aux ports... assuming everything else is stock. You gotta remember it was all calibrated from the factory to work as a team. Once you start messing with it (like me hotrodding this thing) you can no longer rely on these. Thus I'm going to look into feeding exhaust pressure into the aux actuators another way, as I feel it is the only thing I can do at this point, if I want them to be functional. Plus it no longer requires the restrictive mini cast header thing or finding a set of 12AT or 6 port housings which are unobtanium at this point.
One note about this picture and the one above. Notice the owner had used a 79-80 thermal reactor gasket which opened up a fun little exhaust leak that he couldn't figure out how to get rid of. lol
The intake ports are comically and tragically small. Far narrower than anything you've ever seen before. I'll see if I can snap a comparison pic of them next to a stock 4 port 12A.
That exhaust manifold looks pretty cool,how did you come across that engine. I never even knew they made a 6 port 12a until I started reading this thread. Very interesting
04-19-16, 10:07 PM
I then swapped in a set of metric 121 jets in the secondary side for now, to deal with the increased air flow through the GSL-SE end plates. Of course wideband tuning will be required to get the carb just right but this tune is a good place to start.
