AMC 360 - Distributor advance recurve and HEI ignition module upgrade

[jeepnmatt]

With Sandblast 2026 a few days away...i decided to blow-apart my distributor and build an auxiliary ignition system using an HEI module.

Backstory: My Scrambler has an AMC 360 for a mid-1980's Grand Wagoneer. It is a Marshall rebuilt engine from Napa that i bought in the early 2000's and has always run good. The distributor was a rebuilt unit and has always worked OK...except when trying to climb Test Hill at Silver Lake. As i get to the top of the dune at 4000rpm and max load, it spark-knocks from the ignition timing being too advanced and loses power. It has also always felt a little lazy on acceleration, but not bad.

I have a 1969 Dodge Charger with a 440 than i am restoring and found some youtube videos on how to recurve the mechanical advance and why to do it. The ignition systems on those cars were marginal, and found a company that makes a bracket to attach a GM HEI module to the base of the distributor. I did the mechanical advance mods and installed the HEI module and it runs great, so i thought i would do the same to my Scrambler.

This guy has a few really good videos on re-curving mopar distributors and does a great job of explaining how and why:

I also like this guy and watch a lot of his videos. This one has some additional infomation:

this one explains why to use ported vacuum for the vacuum advance:

Here are some videos showing how to take apart the distributor...its pretty easy once you see how to do it. I did buy the battery terminal puller from Amazon for $10 and it is worth it!

https://www.youtube.com/watch?v=VKIzTSsj5yA

in case you are wondering, you do have to remove the distributor from the engine....i'll explain that later.

more to come...

 

[jeepnmatt]

I disassembled my distributor with it in the engine. I found that the mechanical timing limit plate was on the 21 degree side and i had one really heavy spring that has an elongated loop (so it is effectively not engaged until the RPM is up) and the other spring was a medium.

 

[jeepnmatt]

In the photo below, they are the top spring and the bottom spring. The middle spring in the photo is one i took from an old distributor i had in my parts bin and the lightest of the three.

 

[jeepnmatt]

I flipped the limit plate over to the 16 degree setting, stretched the medium spring so it barely had any tension when connected, and installed the light spring. You can also get spring kits from Mr Gasket for around $10.

 

[jeepnmatt]

When i was reassembling my distributor, i found out that the rotor was 180 degrees out of phase...obviously by flipping the limiting plate. So, i had to remove the clamp, pull the distributor up enough to clear the cam gear, rotate it 180, and set it back down. luckily i marked where the rotor was pointing before i started and this only took a couple minutes.

After reassembly, i went for a test drive and immediatley noticed a difference in "pep" as i accelerated!

I forgot to mention that before making any changes, i took advance readings with my timing light both with the vacuum connected and without. The readings i got were consistent with the 21 degrees of mechanical advance and somewhere around 15 degrees of vacuum advance.

When i rechecked the timing after flipping the limit plate and installing the lighter springs, i noticed that the mechanical advance was 5 degrees less and jumped up a lot faster. I have the readings and will post them soon, along with a graph. I am hoping that by removing 5 degrees of advance at higher RPM my spark-knock problem will go away.

I messed with the HEI module, but is is acting weird. The engine will start and immediately die UNLESS i give it a little gas pedal at first to hold it at around 1000rpm for a few seconds, then it will idle like normal. I'll mess with it more at Sandblast next week. Currently it is a back-up system incase the Duraspark module dies.

I'll post the performance results after doing some testing at Sandblast!