Igniting that Carbureted 20V 4AG with "Vintage Fie Yuh"! (fīr)
For those of you foolish enough (to others you are a wicked blasphemer) to go exploring in the old forest of carburetion, hunched over laden with a 20 valve 4AG motor on your back - a treasure that you will most certainly seek amidst those unjustly maligned woods is the "fire of life"...
Okay, so what are we talking about here? We're talking about ignition, folks. We're not just talking about just simply "spark" but also the good stuff that should come with it: timing advance. With a plethora of options available to us today, we shouldn't have any issues solving the problem of ignition for a formerly efi but now carbureted engine. What I'm proposing here is an unorthodox option that is easily attainable, so long as the parts are, and less obtrusive when all is said and done. So enough with the long winded chit-chat and onto the brief explanation that is the focus of our topic.
Here's the scenario: you're in the US, you found yourself in the possession of an SR5 5 speed AE86. Your buddy gave you his Black Top 20 Valve 4AG that's just been sitting in his garage waiting to be put to good use but not by him. You don't want to go through the trouble of sourcing the harnesses from a US GTS or from a JDM AE111 and even if you did you'd still have to modify either harness to work in your FR platform. You got a wild hair of an idea to still swap in the 20V but keep it carbureted because another buddy, who hordes all sorts of automotive/recreational vehicle goodies, just gave you a set of flatslide carbs off of a snow sled that are big enough to match the original throttle bodies that were on the Black Top to begin with. You're excited because you get to keep most of your original SR5 engine harness intact. Then you remembered "...wait, how am I going to run ignition and timing if I'm not going to run the factory ecu?"
Here's the solution - find yourself the distributor from a FWD Corolla outfitted with the 4AF, NOT 4AFE or 4AC but specifically the 4.A.F. engine. It'll be a carbureted version of the 4AFE basically which employed a distributor that uses vacuum and centrifugal advance. Just like its prettier and more desired sister, the 4AG 20 Valve, it too runs its distributor on the back of the head spun up by the exhaust cam end. The engine should have come in the AE92/95 chassis from 1987-1992. Owners of these donor chassis, as well as AW11 fans, would have a much easier time of swapping the 20 valve in and employing the old 4AF distributor than RWD fanatics - it's the whole firewall clearance issue.
The distributor fits perfectly in and can be clocked with the rotor pointing at the number 4 spark plug tower with the engine at TDC. You would just then order the spark plug wires accordingly. The 4AF distributor, with its extra doo-hickies, pokes out more but you can probably smack in that firewall enough to get your clearance. Another option with the 4AF distributor, which I am more keen on, is to: 1. line up the 20 valve motor to TDC and remove the factory distributor (if it came with one or you haven't removed it yet)
2. remove the internal coil from the distributor
3. install the 4AF distributor and clock the distributor to where the rotor is oriented at the number 4 spark plug tower contact (with this alignment you should be able to bolt down the distributor by one of its mount ears while the other one is pointing towards 1-2 o'clock)
4. remove the distributor rotor
5. extend the wires that normally connect to the coil to an external 2 pin connector (preferably the same male/female spade terminals and connector that were on the 4AC distributor - proper pin orientation of course ) and connect to the SR5 harness.
6. fabricate a cap cover for the 4AF distributor
7. get a hold of an external coil of your choice and mount it closer to the front of the motor (e.g. on the left front fender - use either the factory GTS coil or a vibration proof aftermarket coil - they're epoxy filled so you can orient them any way you desire)
8. get a hold of the distributor cap relocation kit from Sam at SQ Engineering and install it.
9. Then arrange the spark plug wires according to the correct AE111 firing order. Here are some pics to help illustrate what we're discussing. Enjoy!
The 4AF distributor fits!
The distributor looks like it's right at home in that 20 valve head.
Let's get her to TDC - good enough for government work.
...now for the cams...close enough.
Well, isn't that convenient - vacuum diaphragms are up, mounting ear lines up. This illustrates the recommended orientation of the distributor.
That coil has got to go, and those wires need to stop hiding from the world.