Metalworker

Hello I just picked up a 1985 rx-7 with a 12a 6 port intake and want to upgrade to a better system but can't find the options for this setup please help thank you also air pump had been deleted too would like to learn as much as possible about this engine or should we just switch it out to a different engine having hard time finding gaskets for it too

Jeff20B

iTrader: (13)

The 6 port 12A is pretty rare. There are cool aspects of it that are upgradable if you choose to do so. Do you have any pictures?

Metalworker

This is a bad pic but pulled intake off to replace the crap they used instead of an actual gasketif there is modes ro do on this intake would like to know what they are already found the mods for the Nikki I have next step while I got this off is to install a header

t_g_farrell

iTrader: (1)

Your in good hands, Jeff can fill you in.

Jeff20B

iTrader: (13)

You are right about the gaskets. I've not located them yet so I was going to do a combination of GSL-SE and 12A paper gaskets. The runner positions are kinda similar enough I think.

This engine uses exhaust backpressure through the ACV channels to open the aux ports. That is why Mazda decided to start doing it more directly for the FC as the channels inside the manifold are cooler than inside the engine and can lead to carbon buildup over time, especially if the coolant temp controlled semi-automatic choke malfunctions and stays on most of the time, as this happened on mine before I acquired it. But upon closer inspection, your carb is probably not original to the 6 port 12A. Yours appears to be an 81-82 from a US-spec 4 port 12A. Someone removed the OMP lifting stuff which is a dumb idea. They also connected one of the nylon lines to one of the OMP nipples. Strange. I also see the emergency return spring rod is just sorta hanging there. That carbs needs some attention asap.

At least the good thing about a US spec Nikki is it came stock with a set of 20mm primary venturis. This is an upgrade from the original 6 port carb which only had 18mm primaries. Can you imagine how quickly a carb that small would run out of flow? Probably goes anemic at 4k or something.

My friend drove one of these back in the day and said all it had was low end torque. Understandable when you look at how small the runners and ports are. Plus the dinky venturis. My plan is to possibly open up the runners to US-spec size if possible and up the venturi sizes to whatever will work best on this engine. Also ditch the stock exhaust manifold in favor of a long primary. As for the aux ports, because I will have fundamentally altered the backpressure they were expecting (reducing it in the exhaust system but also increasing incoming air flow - who knows where the required 3 psi opening pressure will occur in the RPM< range) I was possibly just going to wire them open but I will swap in Pineapple sleeves or the ramped ones from Atkins. I pretty much doubt having all 6 open will hurt low RPM performance but we shall see, as I've driven 6 port 13Bs with a modded manifold to accept a Nikki with all 6 open, and it seemed fine.

Metalworker

ok so if i go with a good rb header should i just open up the 5th and 6th ports so they work all the time or do i just put back together and let the ports work like they should i also ordered a carb kit for this hopefully i can find info about carb this is going to be a fun challenge after all i ever worked on and built up before were v-8's they already did alot of the deletes on this engine

j9fd3s

iTrader: (3)

you could trim down a GSL-SE gasket.

the OE gasket is available, N225-13-111A, https://www.amayama.com/en/part/mazda/n22513111a

mikey D

Making gasket's is pretty easy. I like to rough it out with with a razor and then use a hole punch for the port holes.

Just a thought and it's cheap.