13b struggles fb three questions
 

Since you have a 1990 engine and want to keep fi, you will need to either go aftermarket or use the 1990 computer and wiring harness. The 1990 is an s5 and will require the factory oil metering pump. Even if you want to premix, the s5 oil metering pump will need to at least be connected to the harness.

For the pickup tube, I think you can the one that comes on the 1990 engine.

I have completed the same swap into my 85 using my 88 s4. You'll want to use the 12a pickup tube with the -SE pan.

Wiring was the only part that was really difficult, The only harness that needs to be modified is the one that runs across the dash and through the firewall on the drivers side and the other one can be ran as is. Getting it out takes a bit of finesse and patience. The only difference between the s4 and s5 harness is the electronic OMP that Kansas mentioned earlier. What I did was to go wire by wire on the drivers harness isolating the controlling the coils, main relay, and fuel pump/Circuit opening relay. I de-pinned each wire one by one from the ecu connector, pulled it free of the rest of the harness, then re-pinned it until I was left with the approximately 15 wires that are needed to run the engine, and didn't cut any of them. I then de-pinned the rest of the nonsense wires that work the headlights and everything. At the end of it, I only had to tap into one 12v ignition source wire and my tachometer wire.

The 12a transmission is more than adequate for the N/A 13b, so I just ran it using the Fc's Clutch. If you want to run the Fc's tranny, you'll have to swap the fb tailshaft to it, but I think that's it.

You'll also need to figure out a fuel pump arrangement. Either inline with a surge tank, a fuel cell. or like I did, cut the cup and mount ring out of the Fc tank, and mount them into the Fb's.

Exhaust will have to be addressed as well. The easiest was is to find an -SE exhaust, manifold and all. I used the Fc manifold, and welded an Fc flange to the Fb exhaust, but it has a drastic half inch reduction directly after the manifold that needs to be taken care of.

I completed this swap in about 4 months and only spent about $400. I had an -SE front cover (you can run the 12a cover if you're planning on premixing), so I really only had to purchase the -SE pan, new gaskets, fuel filter, and plugs and wires. It was a lot of work, but well worth it, Nothing was really too hard. Hell, if I was was able to do it, anyone could IMO. The car is a blast to drive, and I feel like I can daily it if I wanted to, actually; come to think of it, I haven't driven my 8 in over a month! . Let me know if you need any more information, I'll be more than happy to help out.

Yeah, I made my own block off plates and did a full emissions delete, but in retrospect, I should have waited until everything was in the car and running. I ran into some vacuum leaks under the manifold that caused idle problems, and had to pull the manifold again.

I forgot that there are a few wires on the 12a system that had to be swapped into the 13b harness so the rest of the gauges work though. The oil pressure switch, temp sensor, and alternator charge signal wire had to be tapped onto the the yellow 8 pin plug coming out of the passenger side firewall.

I also disassembled the fuel level sensor from the Fc pump, and just used Fb's level sensor, but I had to adjust the float rod to compensate for the extra height of the slosh cup.

This thread really helped with the wiring.
https://www.rx7club.com/1st-generation-specific-1979-1985-18/1984-gsl-se-s4-13b-project-832622/

Are your plans to also transplant the 2nd gen subframe?

The advantage of doing the subframe swap is that you get 5 lug/bigger brakes, rack steering, and get to keep the s5 engine mounts. This would save having to swap the from cover and pan. There are several write-ups in the first gen on the swap. I also think the subframe swap also gets you a wider range of coil-over options.

I understand, if I can get the rear axle to reasonably swap too then it seems like a go. I will look into it, appreciate the suggestions. On to research!

That's the fun part! Pull the dash, then start disconnecting at the passenger headlight and work your way around the front, and down the drivers fender. You could really just cut everything after the leading coil and make it easier though. I'd label everything as you disconnect it. Gently pull the harness through the firewall and into the cabin unplugging relays and connectors and reconnecting them as you get them through the firewall. It's tedious, but will save some headaches later on!

The subframe is a good idea, but there's a bit of fabrication involved, and you'd be left with 2 wheel lug patterns unless you come across an -se rear end. In the end, I just decided to keep the front end as is. Having the FC rear subframe would be awesome to have in an Fb with its independent suspension, but I don't think I've ever heard of someone doing it. I did pull mine out and have plans of putting it into my RePu though.

Weber
 

As of now I have installed a Weber ida48. I have also on hand a Holley red pump and regulator. My question is will I use a return? Does anyone have experience with either using one or not using a return to the tank?

You may want to start your own thread but the short answer is use a return to help keep your pump from working to hard. The weber only takes about 3 psi and I'm sure the red pump is rated higher.