Submitted by Guy Kaeser For you folks still using the Motorcraft distributor/ignition system, I want to tell you how to upgrade your ignition system to eliminate the old distributor, coil and “brain box” on the driver’s side fender well. The Motorcraft ignition system puts out somewhere around 17,000 volts, but the stock GM HEI ignition puts out 30,000 volts with stock coil in the cap and one wire to power it, eliminating the old ‘brain box’. It was the most bang for the buck that I have modified on my engine and it’s a very simple conversion, giving you a poor man’s MSD. When I first did this conversion years ago, I was just
getting used to the internet and the info was pretty sketchy starting
first with the American Jeepster Club putting the HEI on a 225 odd fire
V6. One thing led to the next and some California folks did this to
their 258s on a Howell fuel injection forum that I belonged while researching
the use of a Chevy TBI on a 258 with junkyard parts, and I picked it
up at that point. There is a few write-ups on the internet, but I will
give one of the best sites from a fellow named Larry Maggio who did
this conversion at the time I did, he belonging to the fuel injection
forum as well. http://www.geocities.com/jeeperaz/hei.htm GM was way ahead of the high energy ignition game back in the 1970s and the distributor you’ll be looking for is from a 1978-1982 250 ci Chevy straight six engine. These were very common engines in vans and pickups and are like all other Chevy parts, plentiful in the boneyards and parts availability is almost on the shelves at Walgreens (actually, you can probably get GM HEI parts at Walmart). This makes this conversion more practical and repairable than keeping the stock ignition system in your engine GM parts are everywhere! Enough background, now for some meat and tators. Use a GM HEI from a 1978-1982 Chevy 250 ci I6 engine. Beginning in 1983, they began computer controlled ignitions, so this distributor is not appropriate for this conversion. I pulled one from a van several years ago for $40, but have gotten them within the past year for as little as $15. The distributors on these engines are up front under the number 1 & 2 spark plugs and easy to get too. While you are pulling the distributor, grab the heavy wire feeding power to it and cut it off as far back in the harness as you can. Chances are good that all components in the HEI will be in good shape, so do not spend anything on new cap/rotor/etc., until you have determined that what you have is worn out. You’re done here. Next, you want a distributor drive gear from a points type AMC distributor or one from an AMC V8. (When I did this I did not know about the V8 distributor drive gear and spent a little time trying to find a points type gear.) You can order these gears new from 4 Wheel Drive Hardware (part #3208615 - $24.99), Summit, your friendly smiling AMC /Jeep/Chrysler (J)320-8615 (may or may not have the "J" depends on dealer) approx. $40.00 , or pull a distributor out of an AMC V8 (78 or newer) while you’re at the boneyard for maybe $10. Next you will need a set of spark plug wires for a Ford 300 ci I6 engine. These are nice short wires and have the ends that you need to fit the HEI cap and your spark plugs. The Ford engine has the distributor in the middle of the engine like the AMC 258. If you are cheap or you recently installed some new spark plugs, you are good to go. If you decide new plugs, buy stock plugs for your engine and I prefer AC Delco or Autolite. Do not waste your money on splitfire or platinums, etc. You will be putting 30,000 volts to the stock plugs soon and they will come alive. The last item to find is a relay. The GM HEI likes a full 12 volts of power on a heavy wire (10 ga.) I know the old points systems had a ballast resistor so you would get 12 volts on crank, but the voltage would drop for running so you would not burn up the points. The existing wire to power your coil (+ side) is small and cannot carry much voltage, so we’ll use this one to energize the relay. The relay I found was a Mopar heavy duty starter relay and much heavier duty than what’s needed, but I like beef, so I got it. The way a relay works is that it will allow full voltage to flow when it is “turned on” by lesser power to it. I used the wire from the + side of the coil to “turn on” my relay, with the supply wire directly to the positive side of the battery and the other terminal to the HEI. Old ignition wire turns the relay on, and it allows 12 volts from the battery to flow directly to the HEI. Okay, we’re ready to take old stuff off and put your new stuff in. Pull all of your spark plug wires off, remove the spark plugs and set them aside (or save them for trail spares), remove the wiring to the old coil, making note of the positive wire (+). You can tap the starter to bring up #1 cylinder on compression stroke. (If you put your finger over the #1 spark plug hole, it’ll blow your finger away when it comes up compression stroke. If you can’t find it or get close enough this way, turn the engine by hand until the timing mark comes up on 0 degrees. Naturally, before rotating the engine by hand, disconnect the positive battery terminal. When you have found top dead center of number one cylinder with the timing mark and verified it by sticking a small piece of wire into the spark plug hole to verify the piston is up and the timing mark is on “0”, pull the cap from the old distributor, noting the position of the rotor button. When you install the HEI, install it so the rotor is in the same position. Actually, this is to make you feel better. The engine doesn’t care where the number one location is on the distributor as long as the number one wire goes to this position. I actually moved my #1 later for convenience. Without moving the engine, it is now time to install the HEI, since the new drive gear has already been installed, right? If you haven’t installed the drive gear yet, there’s a roll pin through the drive gear sleeve. Note that the 2 drive gears are exactly the opposite. Drive the roll pin out, pull the old gear, install the new gear and re-install the roll pin. Look down into the engine where the old distributor came out and you will see the cam gear that drives the distributor gear and what looks like a large screw at the bottom. This is the oil pump shaft. When installing the HEI you’ll need to roughly line these up, allowing for the twist when engaging the cam gear. It’s no big thing and it’s not complicated, just may take a couple of tries. When you do have a good mate, make sure that the HEI base is completely seated on the engine flange. If it is not flush, pull the HEI and turn on the grinder, grinding away a little material on the shaft blade of the HEI at a time until it completely seats into the engine. Actually, my engine is the only one that I’ve had to do this too, so I don’t know if it was my engine or a freak HEI shaft. Once the HEI is seated, take the old hold down clamp and install it so the HEI is held in place, but remember you’ll have to time the engine so don’t make it too tight. Noting the position of the HEI rotor, install the HEI cap and mark it where the number one (#1) wire should fit. If you’re using the same spark plugs, let’s gap them to .045 and put them in. Remember, we’re going to be firing them with 30,000 volts, so widening the gap will create a hotter spark and a more efficient engine. Put the Ford wires on the engine, beginning with #1 and following the firing order. Now the relay. Remember that little wire going to the + side of the old coil? Run it to your relay’s energizing terminal. Run a 10 ga. Wire from the + battery terminal to the relay and that wire you stole from the original donor Chevy engine to the outbound terminal of the relay and to the HEI. Presto-chango...you now have a 30,000 volt ignition system. After resetting your timing to 6 BTC, unplug the wires from the old brain box and pack them full of white grease or something. I left mine in place for an emergency trail fix, but after realizing how reliable the HEI really is, I quit carrying the old distributor on the trail. The only other thing you will probably want to add is an adjustable vacuum advance by Crane (Summit part # CRN-99600-1). Since the vacuum curve for the Chevy engine is quicker than the AMC 258, you may get some valve ping under partial throttle with the adjustable vacuum advance. I found that using the Chevy springs and weights, I was able to dial in the vacuum advance to find the sweet spot. At any rate, here are the specs for the adjustable vacuum advance from Crane: Cranes Adjustable Vacuum Advance - Spring rates SPRING RPM START ADV. RPM FULL ADV. Blue / Blue 800 3200 Blue = Heavy With your new HEI installed, your engine will start better, run better and much more efficient, so you will be doing your part for the environment. I got tested at a voluntary emission testing station at Walmart in September 2000 with 106,000 miles on my engine. Here are the results: High speed CO - .125% (2500 rpm) The limit is 1 - 1.2 % for CO If anyone has any questions or concerns, drop an email to me and I’ll do my best to help, gkaeser@one.net . Return to Tech Tales Return to Event
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Author: Web4Fam
Revised: May 21, 2004