Rambler 195.6 ignition

Megajolt/E and EDIS-6, and upgrades to the stock distributor

updated 10 april 2019

you can contact me at it is as if at protonmail dot com

the distributor for this engine is a dead end, parts hard to get, new replacements non-existent, and even with Pertronix "electronic points" there is little room for improvement and performance is lousy.

EDIS-6 and MegaJolt

at the moment i have crankshaft-timed spark using Ford EDIS-6 components and a Megajolt controller. i've run this system since 2010. Megasquirt is another way to control the EDIS box. there are now multiple paths to similar solutions. mine is just one path. 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.

external resources

here are some tuning insights that i found illuminating and bullshit-dispelling.

installation

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. i bought the 36-1 gear; i made the adapter. the missing tooth needs to be indexed to TDC. i made this in two stages: with the adapter bolted to the harmonic balancer and the engine rotated to TDC, i could add the ring, index it, mark it, tack-weld it, double-check, then wfinal weld. Ignore my shitty welding.

the sensor-to-wheel gap is small; i'm running .045".

the coil pack and EDIS module is mounted on a hacked up stock EDIS bracket, putting them adjacent for easy wiring. on this engine the oil pump is driven directly from the camshaft, not the distributor, so i was able to just extract it and make a cap for the hole.


2010, 63 American2019, 61 Roadster

in 2010 i installed some used Ford OEM plug wires; they were probably 5 years old then. they were crazy long so i bought replacement MSD plug ends and boots. though they were still fine in 2019 i replaced them with a new set, admittedly partly because they're red. same deal, Ford V6 wire set all too long, and replacement boots. not cheap, about $100, but theey will last 20 years.

Firing order and coil pack wiring

The firing order for all 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 the markings. 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.

AMC six EDIS firing order
cyls... coil
1 + 6 A
5 + 2 C
3 + 4 B

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" in an exhaust stroke. 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.

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.




Configuring the MegaJolt

you need a computer (laptop) to initially configure Megajolt, and then to install and "tune" via spark map adjustment. the Megajolt comes with a default conservative mapping installed; save-to-disk first, then make changes. (i save every day's change in dated filenames so that i can go back if i screw up.)

having run one for nearly a decade now, i suggest that before tuning, that you figure out how to change the RPM bins to match your engine. the 195.6 OHV is a slow-turning engine and i have most of my bins below 2400 rpm. this gives me fine-grained control over the mid-range stuff. the default bins are every 1000 rpm; for this engine only the first three columns are usable!

tuning software

the tuning program for the Megajolt/E is free for download from Autosports Labs, but it's for Windows only. i run only Linux or MacOS, so i wrote my own. it's fine for basic tuning, but it doesn't handle boost and some of the secondary settings. i'll write that code when i need to. it's free and can be found on my github page. feel free to email me with questions about it.


spark plugs

yes, they look like lawnmower plugs. they might be.

these three plugs all work but have different heat ranges. i'm currently running Autolite 437's, heat range "7". however this choice was made when i was making a very common mistake of tuning for maximum spark advance, and too-rich mixture (see related comments in the Weber carb tuning subtopic in INDUCTION. as of this writing (april 2019) i have things far more properly tuned and may want to run the colder Autolite 216 (heat range "6").

however, the Autolite and Champion plugs are not quite the same. i don't currently have any of the other compatibles to check. the difference is in the threaded portion: Autolines have .435" of thread, and Champion .400". the Autolites thread in with the shell flush with the inside of the plug recess in the combustion chamber (i checked on a spare head). the Champion leaves two full threads exposed in the block.

however Champion RJ18YC/J18YC plug has a longer ground electrode and center insulator, which puts it at the exact same reach as both Autolite plugs. RJ18YC is heat range "8" and the insulator is visibly longer.

its nice to have some choice here. the photo below is left to right Champion RJ18YC, Autolite 216, Autolite 437, same as the above photo.







distributor ignition

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 [at the distributor; it runs half crank speed, so 22 degrees advance at the crankshaft]. 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 stock distributor that are fairly easy and worthwhile if you intend to keep it in place.

Improving the old Delco Remy distributor

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.)

Mechanical advance

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. maximum advance is then 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.

  Stock Modified
Static 5 13
Centrifugal 11 20
TOTAL 16 33
(Vacuum advance) 11 11 - 16 (see text)
(Vacuum source) manifold manifold

Optimum static timing is somewhere around 10 - 16 degrees BTDC, for a total of 32 degrees. 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.

Vacuum advance

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.