argatoga

I am thinking of buying a first gen. I happen to have a 12A-SPI (from a JDM Cosmo) with less than 60k laying around. Would there be any difficulties with swapping this in? The previous owner welded the intake so all 6 ports will be open all the time. I have the carb which was stripped by the previous owner.

According to the Internets the engine pumps out ~130hp stock so I'm guessing performance should be close to that of the gsl-se.

Jeff20B

iTrader: (13)

I have a 6 port 12A. Having torn it down, the primary ports are very narrow. The secondary llow RPM ports are the same size as a GSL-SE, as well as the aux ports if I remember correctly. Only the primaries were sickeningly small.

So the plan on my 6 port is to widen the primaries so they open at GSL-SE/12A spec. The original end plates were bad so I swapped to a set of GSL-SE/RE-SI plates so the secondaries don't really need to be changed, but I'll probably do some smoothing and maybe enlarging but it depends on what research I'm able to do in the mean time. I'm also open to suggestions from others who've ported 6 port engines before. This will be my first time.

As for the intake manifold, it's really too bad it was molested. Having functioning aux ports on a 12A will give it the same good low end torque of a 13B, but the high end of a streetported 12A, and the gas mileage of a small ported 12A when you're cruising on primaries. It's the best of all three worlds, which I intend to capitalize on at some point.

Gotta choose the right vehicle for the swap... 1st gen is out since a 13B can go in them easily... Something small... A street bug has always piqued my interest when I thinmk about potential choices for this engine = 12A is short enough to fit under rear deck lid more easily than a 13B, for one thing. One and I've got a nioce high volume oil pan for a 12A that's just aching to be used, which doesn't fit the 1st gen 7 crossmember because it's either from an RX-3 or an R5 12A from a J-spec Cosmo or something.

The carb is another interesting story. It used coolant to control the choke, a bit like the thermowax of EFI engines. Mine may or may not be rebuildable. I gotta tear into it to find out. I've got another 6 port carb that was stripped by the previous owner. It works well enough on a 6 port 13B with a modded manifold.

argatoga

Jeff20B would you post both sides of your intake manifold?

discomatt

If no smog laws You could get 160-180 out of a holley and duals on a 12a without much penalty idling or at the pump. With all the ports wide open it would take a blower to get enough air for decent idle, but then 12a's have always been about efficiency before power (just like every Honda product, ever). Race cars are not that fun to live with as daily drivers, things like cruise control, power steering and A/C don't seem like extra weight when you have to hold the revs above 2k just to inch along in traffic...

arghx

iTrader: (3)

I would love to see pics of a 6 port 12A.

argatoga

Here are some shots I took:

Jobro

iTrader: (2)

I've got 12A 6port pictures which contradict your findings. I've not stripped one myself. But I was under the impression the ports were very narrow but tall all round.

I've seen 3 JDM only plates

13B RESI (JDM Cosmo automatic only) this is different to a US GSL-SE RESI plate btw!
2x JDM 12AT (It looks similar to a standard tallport in shape, it doesn't go down as much but at the same time is really narrow.

Can you post up pics of the 12A 6port centre plate? From pics I've seen it should have an EGR fitting that needs to be blocked off on the top of the centre. Also 'H' cast into the rotor housings. Not sure if 4 or 2 line OMP. There is one I can go look at to buy tho...

Jobro

iTrader: (2)

Is the bolt spacing the same for 6port engines through both the FB and FC era's. Like could you use a S4 or S5 intake on a GSL-SE 6port or a bastard 12A 6port plate build that had 13B housings.

argatoga

Smog laws aren't an issue for me. I was running that 12A with straight pipes before decided on putting a 13B into my MG.

I would love to have it working correctly for the fuel savings. But I'm guessing I'll need to have my molested intake machined.

I do have the H on mine.

arghx

iTrader: (3)

Wow those ports are small. Check out the intake ports on an Rx-8:



It's amazing what 20 years of development (and increased displacement etc) will do.

argatoga

If I get the intake manifold fixed up, would I be able to use the actuators from a 13B six port? I had two 13Bs rebuilt to become one good engine. Since I am blocking off its actuators (properly) and carbing it (clearance issues with the MG) I have lots of engine parts.

argatoga

New idea. Would it be possible to use the '88 EFI system on it?