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HEI Electronic Ignition Retrofit How-To
(Sun Jan 15, 2006 9:08 pm)
|Looking for the discussion thread for this mod?
Looking for the explanation of why HEI is well-engineered?
Why change from a Mopar type ignition control box to a GM HEI module (or why install HEI instead of Mopar)?
This post contains a detailed technical comparison of the two systems. In short, the HEI gives a hotter, longer-duration spark (for better ignition and more complete combustion) and eliminates the ballast resistor (which is a common failure point). Here is a comparison of the ignition performance of Mopar vs. HEI ignition in a slant-6 engine. You can see the HEI spark is of longer duration and of sufficiently high power to support a larger spark plug gap (0.045" is the standard gap on GM engines originally equipped with HEI) for higher secondary voltage:
What you'll need
Use an ordinary Chrysler electronic ignition distributor with a single pickup and vacuum advance. If your car hasn't already got one, you can get a brand new one from Old Car Parts Northwest.
You'll need a good quality HEI module such as NAPA Echlin TP-45, ACDelco D-1906, or Standard-Bluestreak LX-301. If you're doing a high-RPM, max-performance build, there are high-performance modules available, such as Accel 35361, or ultrahigh-performance modules such as 35367. These are overkill (or ultra-overkill!) on the street and out of the wallet.
Mounting the module
There's a bracket available to mount an HEI module to the underside of a Chrysler distributor. This is a nice, clean option for V8 engines whereon the distributor is up top, well away from any possibility of road splash and with plenty of clear space for some extra equipment under the distributor body without interfering with the ability to rotate the distributor to adjust the timing. That's not the case with the slant-6 distributor's low, rather cramped location, though.
The basic way forward is to mount the module to the inner fender or wheelhouse, just above the distributor and high enough up to be kept away from engine heat and road splash. Fetch a piece of aluminum ¼” thick by about 2” by about 3½”. Drill two holes in it to match the HEI module's mounting holes. Heat sink compound comes with every new HEI module. Squirt some onto your mount plate, put HEI module on the plate, and secure the plate and module to inner fender. Strictly speaking, this aluminum mounting plate is optional. It helps assure temperature and mount stability of the module. Some have done the mod by just bolting the module to the inner fender and had acceptable results.
Your stock coil might work OK for awhile, but really isn't a good choice. At the very least, replace it with a coil meant for use with electronic ignition. Such a coil would be a Standard-BlueStreak #UC16 or NAPA Echlin #IC27. It's best, though, to use a coil intended for use with a high energy ignition system. If you'd like to mount the module off by itself somewhere, then a good coil option is the stock external-mount E-core coil used with Ford and Mazda high-power electronic ignition systsems. The premium version is Standard BlueStreak #FD-478X:
You can save eight whole dollars by specifying the ordinary FD-478 (or NAPA Echlin IC-24) instead of the premium FD-478X, or you can save a whackload of cash by specifying the cheap Chinese FD-478T or NAPA Echlin IC-24SB (not recommended). If you're going yard-hopping, you'll find this coil in '82-'97 Ford cars and trucks, '84-'94 Lincolns, '82-'95 Mercury and '85-'89 Merkur models, as well as '94-'97 Mazdas. You can grab the connectors and a few inches of primary wire, as well, or if you'd like to have a new connector with wire, use Standard #S-539:
Another workable coil is the GM HEI coil used on '75-'84 GM cars mostly with 4-cylinder engines, Standard #DR-35 (no premium "X" version available) or NAPA Echlin DR-35.
A tidy option is to use the combination HEI coil/module/mounting bracket originally found in just about all gasoline-fired GM pickups and RWD SUVs from '96 to at least '00. It includes a nice sturdy mounting bracket, heat sink for the module, E-core ignition coil…all in one:
Wherever you are, you can probably pull these out of wrecking yards all day long for very little money, and you can just grab the watertight connectors for the coil while you're there. This way you take advantage of GM's own work. The newer style module included with this setup (and shown in the photos above) won't work with the Mopar distributor; it's looking for a 0-5 volt square wave, and that's not the kind of signal the Mopar distributor puts out. You can use the early type (4-pin) module—part numbers specified above in the discussion of module selection—on the newer heat sink bracket with minor mods to the heat sink. Then just bolt the combination module/coil/heat sink unit to the inner fender:
If you use this combination coil/module assembly, the original coil has three terminal pins:
A is the coil's primary (+) terminal; gets ignition-on 12v and is connected to module pin "A".
B is a tachometer signal output. Not used if you don't have a tach.
C is the coil's primary (-) terminal, goes to module pin "D"
The only other "gotchya" is that many of these E-core coils have a male (spark plug type) output terminal rather than the female type on our original coils, so you'd need to get an appropriate coil-to-distributor-cap cable such as NAPA Belden #701050, which is a Ford item, or the equivalent from Magnecor or your favoured spark plug wire supplier.
A proper module ground is important. It's rather difficult not to have this just by installing the module, but it's best to run a ground wire to one of the module mounting bolts just to be sure.
Hooking it all up
Remove the ballast resistor from the vehicle. Discard it. Take the two connectors that used to connect to the resistor, and connect them to each other instead.
Hook up the module: Holding the HEI module with its convex side down or toward you, the upper left is terminal “B,” battery; lower left is “C,” trigger; and the two on the right are for the distributor pickup coil. Which pickup coil wire goes to which module terminal is determined by trial and error: If engine is difficult to start or runs poorly after installation, you swap these two wires.
So, the two wires from an ordinary Mopar electronic distributor go to the module's two right-side terminals, the module's upper left “B” terminal gets connected to coil (+) primary so that it gets +12V from ignition switch with no ballast resistor in between, and the module's terminal “C” goes to coil (-) primary.
You'll want to add a power relay to guarantee full line voltage to the ignition module at all times. If the ignition module is starved for power, it'll work unreliably and it'll die prematurely. The module really needs to see full line voltage, and the wiring in most of our cars isn't up to that task after all these years. So, when setting up your module wiring, it's best to install a relay that'll provide full line voltage to the module via the coil + terminal.
Use a good brand of relay (Bosch/Tyco, Omron, and Hella are three good picks). You need an ordinary 4-prong normally-open ("SPST") relay. The prongs will be labelled #30, #85, #86, and #87.
#30 is your power input. Connect this via a 14ga wire to a good, solid source of line voltage. Good options for where to pick up this power feed include the battery positive terminal, alternator B+ terminal, large terminal on the starter relay, large terminal on the starter. Put a fuseholder in this wire as close as possible to your power takeoff point. You'll want a 15A fuse, and you'll want to carry spares.
#85 is your trigger ground. Run a 16ga wire from this one to any decent ground.
#86 is your trigger feed. This one needs a 16ga wire that's live when (and only when) the ignition is switched on.
#87 is your power output. Connect this via a 14ga wire to the coil + and to the module's power terminal.
Here's an annotated diagram of an HEI installation on a 1965 Dart. On this particular car, the installation was done in conjunction with some other electrical modifications not part of the HEI job, such as the addition of a master fuse panel under the hood:
• Here is a thread with pictures and a video link, describing a low-dollar HEI installation.
• Here is another site with instructions on how to do this swap. The author of the linked page says you have to have the GM module connector, but that's not true. All you have to do is make sure you use the correct-size female spade terminals (three of the four terminals on the module are ¼”, while the fourth is 3/16”.)
• The improved spark quality with HEI permits you to increase your spark plug gaps from 0.035” to 0.045” for improved starting, idling, driveability, and mileage. If you're running the 1960 to 1974 cylinder head with spark plug tubes, now's a good time to put in a set of the extended-nose spark plugs for further driveability and mileage improvements. My preference is for NGK ZFR5N. Remember, if yours is a 1963 to 1974 head, remove the spark plug gaskets; they're not used. If yours is a 1960 to 1962 head, you do need to use the spark plug gaskets.
• Hotter ignition spark comes with a price. It's a small one: You need to pay more careful attention to the condition of your distributor cap, rotor and spark plug wires. Why not change 'em out while you're at it? The trick piece in this department is a NAPA Echlin long-tip rotor # MO-3000, which has a brass contact 0.060” longer than stock. This means less arcing inside the distributor, which means less burn wear on the cap and rotor contacts and less ignition noise in your radio, too! Be careful about Echlin or Accel distributor caps, though; many of them are ground off-centre and can cause carnage when the rotor—especially the longer special one—hits one of the improperly-ground, too-big cap contacts. The safer alternative is a Standard-Bluestreak CH-410X. Spark plug wires? Well, go big or go home, right? Get Magnecor wires and you won't have to think about your spark plug cables again for a very long time.
• Drive and enjoy!
Looking for the discussion thread for this mod?
Looking for the explanation of why HEI is well-engineered?
Photos and info courtesy McNoople, DonPal, and Olafla
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Last edited by SlantSixDan on Sat May 03, 2008 9:03 pm; edited 7 times in total