updated 19 mar 2019
you can contact me at it is as if at protonmail dot com
this page covers improvement to the barely adequate stock distributor and points. though i iniitally hacked the original distributor somewhat (see far below) i now consider anything beyond a simple Pertronix upgrade to be a waste of time.
crankshaft-driven spark is no longer exotic. once you get over the admitted hassle of affixing a 36-1 wheel and sensor the rest is a no-brainer, thoguh it will cost you $200 for the aftermarket controller. in exchange you'll get a drop-dead-reliable, zero maintenance ignition and probably some free horsepower (that was lost by the primitive OEM system).
these are tuning insights that i found illuminating and bullshit-dispelling.
at the moment i have crankshaft-timed spark using an adapted Ford EDIS-6 system and a Megajolt controller. i've run this system since 2010.
you can also use Megasquirt or other DIY aftermarket systems to control the EDIS box. there are now multiple paths to similar solutions. below, here, is just one path.
If you aren't familiar with EDIS, a good place to start is the MegaSquirt page. It's a great system, and has been adapted to lots of orphan cars. It puts out as much spark power as many high-performance aftermarket ignition systems, for a fraction of the cost. And for old or odd cars, you get to ditch worn out, hard to replace and frustrating distributors.
The Ford EDIS ignition is easy to adapt. The hardest part is the trigger wheel mounting, but a simple adapter lets you bolt one onto the harmonic balancer.
I bought a "kit" of EDIS parts from Boost Engineering if you are less lazy than me you can scrounge 'em from a junkyard or pick from eBay. I got a coil pack, 36-1 wheel, sensor, wires, all in one batch. Clean and tested good, and still in use 9 years later.
The hardest part of the job on this engine is mounting the sensor and 36-1 wheel. When I rebuilt the engine, i fabbed up a nice clean stiff mount for the sensor and welded it onto the timing chain cover. It would not be all that hard to work up another solution with the engine in-car, probably from below. it's a little tight in there, as you can see from the photos (the one on the right was taken from below).
The mount for the sensor (pickup) is straightforward when the timing cover is off the engine:
here's the 36-1 ring to harmonic damper adapter. Ignore my shitty welding.
I chopped the mounting ears off the provided bracket, welded up new ones to mount it to the inner fender and accept the EDIS6 module, to create an ignition module I could wire up on my bench.
The end result was a neat package with four wires to pierce the firewall, and a short cable that runs to the pickup.
Pay a lot of attention to grounds and shielding! The signal from the pickup is weak, and susceptible to noise picked up in the wiring. The MJLJ documentation is fairly clear here, but I as always go for overkill. All of the grounds -- coil ground, EDIS module ground, and MJLJ module ground -- were short heavy wires, twisted and soldered, with crimped lugs soldered, and screwed to the inner fender in one spot. A #14 wire was run from there through the firewall for the MJLJ box -- do not ground it "conveniently" under the dash. I extended the pickup shielding up to the EDIS module connector using aluminum foil -- it looks rough in the picture above (I wrapped #22 uninsulated wire around it for an electrical connection, then 3M electrical tape for mechanical strength). Overkill for sure, but I've mounted the module very close to the spark coils, there's a lot of energy in the air there. Easy to do now and avoids trouble on the road!
The wires that came from Boost Engineering are crazy long, and loop all over the place. I've ordered a set of replacement MSD spark plug boots from Summit, I'll shorten them up, that will tidy up this mess. The distributor hole plug was simple, just a flat piece of cold-rolled stock cut to fit and silicone sealed.
The sensor to 36-1 wheel gap worked out to be .045".
Drilled a 9/16" hole in the firewall for the harness, mounted the MJLJ box under the glove box. Wired up everything but left the SAW signal (MJLJ control signal to the EDIS controller) disconnected so that EDIS would run in stand-alone "limp home" mode. Much easier to test one thing at a time.
The firing order for all Rambler and AMC sixes is 1-5-3-6-2-4, clockwise crank rotation, counterclockwise distributor rotation. The EDIS coil pack is marked, but it's for the wrong engine; ignore it. The proper wire order for all AMC sixes (1950 - 1989) is below, but working it out from first principles is easy.
Inline sixes have three pairs of cylinders. Each pair of pistons is 120 degrees apart on the crank, and is in the same physical position in the cylinder, but each in the pair is two strokes apart through an Otto Cycle; eg. one on Compression while one on Exhaust.
It's easy to determine which cylinders fire when: for an overall order of 1-5-3-6-2-4, the pairs are: 1 & 6, 5 & 2, 3 & 4. Look at the top of the distributor cap: note that starting with #1, 6 is directly opposite 1. Next is 5; 2 is opposite 5. Next is 3; 4 is opposite 3. Those pairs are the ones with the pistons at the same position in the cylinder.
EDIS takes advantage of this physical pairing. By firing both cylinders in a pair simultaneously, it doesn't need to know camshaft position, only crank position; when the pair approach TDC one of them is in compression stroke, so sparking both lights it off without knowing which. The other spark is "wasted". This vastly simplifies the ignition, and triples the time to saturate a spark coil, each coil is smaller, lighter, runs cooler. Win win win.
Wasted-spark lets you re-think what firing order even means. Because it fires each cylinder twice in an Otto Cycle -- compression and exhaust -- the firing order is really just three pairs, not six individual cylinders. EDIS 6 coil packs are marked A, B, C. EDIS fires them in this order: A, C, B.
|AMC six EDIS firing order|
|1 + 6||A|
|5 + 2||C|
|3 + 4||B|
Six cylinders, but only three engine revolutions, a coil firing every 120 degrees. It doesn't matter which terminal of the coil you wire a cylinder of a pair to! As long as cylinders 1 and 6 go to coil A, etc, it works. Electrically it doesn't matter, but under the hood it means you can attach plug wires so that they're neat and don't cross.
Once wired up as a module and installed, there are four wires that go through the firewall (+12V switched, ground for the MJLJ, and PIP and SAW in a shielded cable), and the sensor cable. That's it! The engine started and idled first time. If it backfires, you may have the firing order wrong, or the trigger wheel positioned badly (the MJLJ installations are pretty clear). If it doesn't fire at all, you may have the sensor wired backwards (swap the wires) or the sensor is too far from the trigger wheel.
It goes as the MegaJolt documentation says. I am very comfortable with computers, but I deeply want to keep computers out of my old cars... but it sure is nice to have precision ignition timing! And tuning the MegaJolt is easy, there's just not that many variables or complexity.
Laptop, Keyspan serial/USB adapter, and the MegaJolt configurator program downloaded from their site. Easy enough. I created a spark map by the seat of my pants -- well not really i know how my distributor is curved from spending so much time with it (and taking notes...)
The first thing I did was to change lobal stuff (number of cylinders, normally aspirated), and the axes of the map -- the default is 500 to 9500 rpm (YEAH RIGHT!) and load 10 - 230 (1 atmosphere boost). I changed rpm to 500 - 5000 in 500 increments and "load" 10 - 100 (103KpA is atmospheric pressure, eg. zero vacuum).
Second I verified that the sensor and 36-1 wheel are aligned right -- i entered 0 in the lower two high-load spark map boxes, uploaded it, and with a timing light looked at the timing marks. My system was off 2 degrees. There's "timing mark" global setting. Nice!
Now to make the initial map. I started with what I know as good starting points for the four corners of the map. These are numbers you will be familiar with if you're comfortable tuning your engine now.
The first thing to set is the load=100 horizontal row of values -- this is pure mechanical advance, eg. a distributor with the hose pulled off. Mine, 500 rpm is 10 degrees advance (static setting), 2500-5000 rpm is full advance (22 degrees, what my hacked distro did). I simply interpolated values by eye, 1000 - 2000. Somewhere, I actually measured this with a hand vacuum pump and a timing light, I'll pull out my notes sometime and look at it, but i recall it being more or less linear.
The far "corner" of the map -- high rpm, low load (high vacuum) -- that's total mechanical advance (static 10 + 22) plus full vacuum advance (11) or 44, 2500-5000 rpm gets that value.(That's a hypothetical, it's unlikely you'll run it > 2500 rpm at high vacuum; in fact I entered lower numbers 3000+).
The other "corner" -- idle, high vacuum -- where a distributor you're always fiddling with "ported vacuum" vs. manifold vacuum you get to actually set it directly, no more compromises. Often, full vacuum is too much, and no vacuum too little. Initial experiments determined that 18 degrees total advance "seems nice" (utterly unscientific, but a starting point).
From there I simply eyeball-interpolated the center of the table; the low-load runs from 18 degrees advance (500 rpm) to 33 degrees (2500-5000 rpm). from that basis on-the-road tuning ended up at this in 2012:
in it's current (april 2018) state of tune, with T5 transmission and 38/38 DGV carburetor, much more aggressive spark timing is needed:
they look like lawnmower plugs. short reach. here there is actually a tiny amount of choice in heat range. "heat range" indicates how much heat the working tip of the plug retains; "cold" plugs run cooler, usually because they have shorter, fatter center insulators which cause the obvious heating from combustion to be wicked into the plug body and the block; "hot" plug tips run hotter which helps burn off combustion products that might accumulate on the tip.
heat range used to matter more back when gasoline left deposits on plugs. it doesn't any more. new gasoline formulations burn incomparably cleaner than the past (regardless of all the complaints about new gas being lousy). i'm running Autolite 437's currently. i'm not sure how much it matters.
the following all work: Autolite 216 is heat range 6, Autolite 437 is heat range 7. NGK B-4L/3112 is heat range 4. Denso 6013? Champion RJ18YC.
my plugs seem to last forever since they don't crud up from the gas. these days i'm changing them annually as part of winter prep for the next year's driving.
the factory stuck an application-specific Delco Remy distributor and coil and points, mechanical and vacuum advance, on the passenger side of the engine. the distributor is extremely spark-advance-limited, 11 degrees maximum mechanical advance. no other distributors known to "fit in the hole". the L-head version of the engine uses an incompatible Autolite distributor inserted into the drivers side of the block. the hole for this is still present, filled with a plug, i suppose with some effort you could run two distributors just for perversity.
a Pertronix module will solve the limitations of points, but my testing has shown that wear in the distributor itself (since new ones are not available), which shows up as timing jitter and weak spark, combined with the utter lack of total spark advance (some 22 degrees), is a major performance limiting factor. consider also that insufficient spark timing adds a lot of heat to the cooling and exhaust systems.
however there are mods and improvements you can make to the
The first order of business is to pitch the points. You can't even buy good ones any more, the aftermarket parts are all crap. While the speed this engine turns (red line is 4500 rpm) isn't pushing things a Pertronix Ignitor, part #1162A, ("Delco 6 cyl with vacuum advance") and the matching epoxy coil is substantially hotter, and more reliable, spark without being wasteful (and arcover-inducing) overkill. (One annoyance with the Pertronix is that you have to file a small clearance notch in the cap to clear the two wires that now come out; if I had thought ahead I would have looked at drilling the distributor body.)
|(Vacuum advance)||11||11 - 16 (see text)|
Mechanical advance on these old Delcos is limited by a pin on the points-cam assembly that lives in a hole on the main shaft assembly. The pin is small, the hole large, so the hole limits rotation to 11 degrees. Enlarging the hole is obvious, but too much and the fly weights will hit the housing. Enlarging the hole is obvious, but total advance change is limited by the weights hitting the distributor case in the outward direction, and the weights hitting each other in the retard direction.
I drilled the hole out to 33/64ths (the parts are all hardened, but I happen to have a carbide-tipped bit that size) and sparingly ground the tips of the weights such that they would fold in closer. I stuck some random soft springs from who-knows-what distributor curve kit, which got the advance to come all-in around 2000 rpm, about right for this motor.
Optimum static timing is somewhere around 10 - 16 degrees BTDC, for a total of 32 degrees. It still never pings. It could use more. I did some before and after 0 - 60mph tests which were inconclusive. Mileage has been steadily creeping up with no carb changes, so that's all good.
If you need to do this to another random distributor, watch for the weights hitting the housing; that's the advance limit. I got a few more degrees out of it by grinding the tips from the weights that allowed them to fall all the way back against the cam; otherwise, the weight tips touched the housing.
Here is maximum and minimum spark advance (minus springs and retainer). Max is limited by the hole (see below) and minumum by the weights hitting each other. Under the rotating assembly you can see the pin and hole that limits advance travel.
Here's the hack. It's not a big deal. A hole drilled, and weight tips ground and checked, repeated until the weights laid flat on the cam. Removed about 1/16" at the tips where indicated.
Hint: when you are fiddling ignition timing, drive around with the vacuum advance hose removed and plugged. Vacuum advance is for part-throttle (high vacuum) cruise only, and doesn't affect power, but will affect drivability or pinging when it's wrong, and it complicates things. Mileage will drop but it greatly eases making adjustments -- one variable at a time.
It turns out, you can easily get 16 degrees vacuum advance by filing the limit-stop down (see below) but don't bother -- once you've upped overall advance, the engine will not tolerate a lot of part-throttle advance. Stock is fine here.