So I'm gonna go 4 port on my 85 se by using 12a irons. my concern? The set of irons I'm gonna look at are "tall port". Can I still run them? does racing beat make a tall port manifold for Webers? I called racing beat and the guy didn't even know what a 12a tall port was. Someone help me out pls...

 

i'm also unfamiliar with a tall port 12A iron. please enlighten me.

my question is why not use a 4 port 13B from the 70's? may be tough to track one down but not a hybrid.

 

A 4 port 13B from the 70s is just a 12A with wider rotors. Same side housings.

Starting with GSL-SE and RX-7 12A parts gets you the best/most common (ha!) rotor housings, and hardened side housings.

Every RX-7 12A I've seen had very tall primary ports, maybe this is what was meant. Don't worry about port mismatch, it's beneficial.

Trivia: The primary runners on my RB 4-port 13B Holley manifold are the same size and placement as GSL-SE primary ports. EXACTLY. I had to open up the runners in the primary ports significantly in order to get a desirable amount of port mismatch. A 12A center would be much better, but they don't have provisions for injectors or motor mounts.

I LOVE this engine compared to the 6-port engines I've had. Would build again.

 

peejay, are you talking about 12A end plates with a GSL-SE intermediate? And GSL-SE rotor housings with an FC rotating assembly? This sounds like a great combination if you want to run EFI and have a need to mount the motor at the middle. Is that how your current nice engine is set up?

 

That's what it is, although trying to mid-mount using GSL-SE center housing isn't working too well. The passenger side mount breaks constantly. I need a better solution to the problem.

More and more I think the solution to my constant transmission problems involves the number six and the letter V, so I'm not really worried about engineering a better solution than periodically rewelding it/adding beef-metal.

 

The iron itself doesn't break, does it? When I went to assemble an engine earlier this year with a GSL-SE intermediate plate, it was cracked along the ACV channel (vertical). I looked at another plate and it had the same crack in the same place.

 

I've never seen that, but I do have a broken S4 T2 center housing, cracked horizontally just above the oil pan rail on the ports side. I globbed silicone over it and used it anyway.

I keep breaking the mount bracket itself. It started out as a FC driver's side mount, but over time it got braced and plated so many times that it's not really recognizeable. It's just too small of an area at the engine to deal with the compressive loads. The driver's side is loaded in tension, that's easy.

 

I'm planning on making a 4 port intake adapter to my 6 six port engine and noticed this too, my current plan is to include a pretty steep opening to them. Did you close off the aux ports?

 

There are no aux ports in a 4 port engine.

 

I know that. My adapter is a small block that the intake bolts to and then that is bolted to the engine. So on that block I could make the ports big enough to include the aux ports, like the one tweakit was selling before they went bust. The intake is for dual DCOEs so the adapter can not be very long to smooth out the transition.

 

Then what's the question about aux ports, then? There aren't any, it's a four port.

 

Never mind, I thought you said you put a 4 port Holley intake on a GSL-SE, somehow missed the part about having 12A rear and front plates.

 

My 2 G-SE's have had 4 ports for it seems like forever now LOL. Opening up those 6-ports isn't always easy....

jerij

 

PeeJay, one thing you could do to strengthen that egr port on the center iron is to sandblast it clean an fill with Devon putty. That should help reduce the load on that thin casting to a larger area.

 

I have been collecting parts and im ready for a rebuild kit but im stuck on which to buy, can i just buy a kit like this from atkins?

74-78 13B Overhaul Kit C (ARE29)

or do i have to go around and mix and match gasket kits and seals etc?

i basically have everything i need, a set of 12a irons (btw were all 12a's the same? if not, then i hope i got the right irons) a complete GSL-SE motor, extra set of low mileage SE rotors and soon a pair of new SE housings. ditchin the efi to go carb. any input would be greatly appreciated.

 

after all the years, I've spent messing with these things, I've learned not to think that there is ever one "order" that gets you from point A to point B. so i'll answer your question like this: it looks pretty comprehensive in terms of what you should need to put the engine together and attach all ancillaries, but you may still have to order or make a few minor things to suit.

 

I'm going over these same questions myself at the moment.

I have a running 12A in my '85 GS with 133K, never had a trouble with the engine,
And it's been in my possession for most of the last 100k miles.

I also have a complete '84 6-port 13B which was running fine when I pulled it from a donor car years ago.

Rather than mess with both, I'd like to combine the two to make a 4-port 13B.

Street porting is a definite, as well as an aluminum flywheel and 45 DCOE, if it's a big enough carburetor. I'm planning a full rebuild with re-surfacing of the irons.

I know I have much more to learn, but currently I think all I have to do it move the 12A irons over the the 13B. And block off the injector holes.

Is it really that simple?

btw: this isn't a daily driver. After reading up on opinions regarding street vs bridge, i'll stick with SP. I just don't want to run a open exhaust to get the full benefit of the BP.

 

My BP is very quiet with the full RB exhaust. Probably will be 250hp when I get enough injector under it and have a proper timing curve. And THAT is only limited by how far I feel like revving it. I don't want to take it up past 9500 but it wants to even when running dead lean because the injectors are static!

That said.... a 45 DCOE is just about right for a stock 12A! You'd want a 50DCO to get the full benefit of a 13B especially with porting.

My bridge ports are the same size as the street ports I used to have, that engine made similar power to what I have now but power peak was 1000+rpm HIGHER (injectors were only at about 90% at 9300rpm, I'm at 90% at maybe 8000) and it didn't make much power below 5500. Better than stock but nowhere near the instant rush of torque everywhere that the bridge port provides. I'm also on 4x42mm throttle bodies (aka a fuelless Holley 750) with fuel injection, which REALLY tames the port drivability-wise.

 

thanks everyone for the input it was much appreciated.

so i went ahead and bought my atkins kit yesterday. today, out of sheer luck i suspect i threw an apex seal. pulled out of my local shell, hit the powerband in 2nd gear then POP! lawnmower like rumbling and a huge loss of power. going to do a compression test tomorrow morning with SoCalFC to confirm.

 

well, the apex seal is done. its confirmed, another FB down for at least a few weeks if not longer. surprisingly, nothing else is wrong with the motor. the single rotor starts and runs every time and the cooling system works fine. ill probably be back here for questions come rebuild time.

for now heres a pic of us replacing the water pump for the first time on a 13b. please pardon my filthy parts car, ill rinse her off tomorrow.