CC Tech: 1973 Dodge Polara HEI Ignition Conversion and Motorcraft 2150 Carb Adaptation

When I first bought my 1973 Dodge Polara Custom Spring Special, I was aware it had the Mopar electronic ignition. However, my Fords all have a 12V Pertronix system installed and I like how it runs. Little did I know the adventure I was in for both with the ignition and the Holley 2bbl carburetor.

Having been in hibernation the car needed some mechanical work as you could imagine. Right off the bat the 50 mile drive home, for my brother, was a bit dodgy given the very soft nature of the master cylinder. Nonetheless, he being a pro he made it fine. Naturally the master was the first thing replaced. Brakes then gone over. After that all the hoses and basic fluids throughout the engine. New tires were on the menu to replace a mismatched set. Now I could drive the car and noticed that there were issues with the acceleration pump on the stock Holley 2210 carb.

This is the little devil. At the time I didn’t know that many of the rebuilt ones never had the top plate trued to be perfectly flat. It seems that when you tighten down the air cleaner the bolt pulls on the top plate where it anchors. So I had three of these carbs with various problems from accelerator pump issues to erratic vacuum leaks. I got tired of this and wonder why Holley couldn’t make a 2bbl. as reliable as the Autolite 2100. Hey now that is an idea.

So I proceed to move onto the project when I now really notice the bases are different. Square bore versus spread bore. Moving onto eBay I find a square bore to spread bore carb adapter. That solved I found a nice rebuilt Motorcraft 2150 and everything hooked up except the hose for the EGR port. Motorcraft doesn’t have a port but no matter as the carb runs perfectly in all aspects. Of course my next problem was an air cleaner to fit the Motorcraft base versus the smaller Holley base. Took some doing finding an appropriate Mopar 4bbl air cleaner. I know but it works.

Now the ignition. I started to have issues with the stock ignition and the car wouldn’t start with the key in start. I wasn’t getting anywhere near 12V. However, if I used a remote starter and put the key in run the car would start fine. So I proceeded to install a Pertronix II after figuring out how to find the 12V wire for the Pertronix coil. Took some doing but I got it done yet still the problem of not starting with key in start. Fine with now and I’ll use the remote inside the car. However, over a two year period the car burned out three modules of which Pertronix replaced two. This could get expensive. On top of that I was checking air pressure in the tires and used the my little pump that plugs into the lighter. When I turned it on the car went poof as in no electrical power via the ignition switch. Ugh! Fuse? Nope they were fine.

So I went through everything and replaced all the old fusible links. Cleaned the bulkhead connector. Replaced the ignition switch and then noticed what was under my dash. There is a connector that has eight wires with one being the main power. The main power had been bypassed given the scorched nature of the connector. Looking above there were the two halves of the main power wire tied together with a twist on wire cap. Ugh! Fixed that and my car was starting again still the typical way.

Now I studied up on how to do a HEI conversion to achieve my 12V ignition. Saw a post in an A Body forum about it and so I adapted it to my car. Bought an E-coil, an ignition module, the wire harness to go along with the Bosch (Tyco) relays I have in stock.

Then I drew out a schematic of my installation to follow.

The 15 amp AGC fuse.

I located this cool base for mounting the electronic module onto the bottom of a Mopar distributor utilizing the two holes in the base. The original black plug did have to be cut off in order to utilize two spade connectors which were needed.

Now the E-coil was not a canister so I had to figure out how to mount it. I didn’t want to put it on the firewall or fender as being too obvious and long distance. The original canister mounts via two bolts, at different heights, on the 2bbl manifold. Hmm, maybe I can make something. So down to the USS Hornet on one of my Saturday volunteer days and into the aircraft metal shop to look at scraps. I find a piece that is just wide enough and long enough of 6021 aircraft aluminum. I use the brake to put a bend in for the base and then go down to the machine shop to cut out a square opening for the coil. At home I paint it semigloss black and mount the coil with stainless steel screws and lock washers.

Time to put the relay in. Use a mounting point next to the ballast resistor. Next, wire up the relay as per my schematic using shrink wrap connectors. Tape off the tach wire. remove the ballast resistor and make bypass connectors. Install correct coil wire to distributor. Last go over everything one more time checking each connection start to finish. See no issues as I have put relays in the car before to run the headlights. Remove spark plugs and open gap from .035 to .040 for now. Starter is now a new Denso high torque mini which took a little doing to connect the cable. Years later I see there is an adapter made to re-position the lugs on the starter.

Houston we are now ready for ignition sequence. Multimeter in place? Check. Starter fluid sprayed down into the carb? Check. Pedal pumped three times? Check. With some trepidation, there is always some trepidation on the launch pad, I will use the key and turn to the start position. Within a split second the engine is on. I mean it is on so fast I never heard the starter turn. Wow, it was like it was always on. The sound through the new dual exhaust and 20″ Dynomax mufflers is a low rumble.

I get out and check my multimeter. I am getting 13 V through the coil to the distributor and the plugs. With the Motorcraft and HEI ignition there is a real difference of how the car runs on the freeway. The engine also continues to start instantly. More instantly than the 2018 Mazda, the 2004 Le Sabre, the 2004 Focus or the 1991 626. Only the 68 Cougar with a Pertronix II and solid rebuilt J code heads starts almost as fast.

As of now I could just continue to drive the car as is. Mechanically there are only a few things left. This spring the U-joints will get replaced. Might get ambitious and go through the A/C system and recharge with R12. Yes, I have the needed tools and refrigerant. Even more ambitious would be the front suspension bushings as I did on the 67 Park Lane.

Years earlier the original interior cleaned up well after removing everything for sound proofing and carpet re-dye. My headliner and vinyl roof were replaced by my guy who does upholstery work from his garage. Excellent work I may say. The vinyl roof was done after I did the body work and paint job on the car. Never had painted such a big long car, all at once before, but managed just fine. Up until then it was only an 8 foot bed of my 65 F-100.

However, there is one more thing lurking in the back of my mind and that is rebuilding the engine while I still can do the physical work now rather than when 75 as I have this and the Mercury 410 left. Might even use the chance to stroke the engine out to a 408 and raise the compression but leave the 2bbl carb so no one is the wiser. We’ll see…