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HEI Distributor Advance Curve

 

I recently fitted a HEI distributor to my car. This gave the benefits of removing the external ECU, ballast resistor, etc. The HEI distributor is completely self contained and only requires +12v, earth, and a cable to the rev counter.

The only issue was the size...
There was a noticeable improvement in the engines smoothness and starting, so worth the work, but during the tune up process I noticed that the advance curve was very, very, slow.

Having previously experimented with faster ignition curves

Advance Curve

Adjustable Distributor

I wanted to change this, so I bought a Proform 66948C HEI advance kit

This comprised 2 new advance weights, and recurved centre plate, and 3 pairs of springs of varying tension to control the advance rate.

The instructions were very, very poor, so I did a bit of digging. It seems that this kit is a generic kit, and is repackaged under a lot of different names. They are all the same equipment, but some come with better instructions

Accel Instructions

MSD Instructions

Allstar Instructions

All 3 instructions called for the heaviest springs for Big Block V8s, which were super slow rate advance. From previous experience, this was way too slow for good throttle response and performance. I decided that the lightest springs would be better for what I was after.

The other thing to note is that in the Allstar instructions, it was the only one that mentions dizzy rotation direction. The instructions show a picture of clockwise rotation. Mopar dizzies are anti clockwise, so the components (centre plate and  centrifugal weights) need to be fitted in reverse.

Stock advance springs and centrifugal weights



Performance advance weights and springs. In the end I went for 1 gold lightweight, and 1 silver medium spring to give fast initial advance, then slow down to prevent pinking



Instructions showing clockwise rotation



The plan was to set this system up with this to start and get some general settings, then add a new stop bush to limit the total amount of mechanical advance.

https://www.ebay.co.uk/itm/235674846966



These can be used to limit the amount of mechanical advance from the standard 22 degrees to either 10 or 14 degrees.

The car started on the button, and ran really well, so time to add the new stop bushes.

Except that my model doesn't use stop bushes. Bugger...

A quick internet search revealed you have to make your own stops, so I had a look at how to do it.

In the arms that the rotor arm screws onto are a pair of unused holes shown with the red arrow below



These can be used to add stops to limit the amount the centrifugal weights can move. I moved the arm to full advance and marked it with a pencil line. Once the arm was returned to the idle position, I measured how much it moves from idle to full advance, which was 10mm

The dizzy gives 22 degrees of advance as standard, so if I limited it to 5mm, that should be 10 to 11degrees, which is what I was after.



After a bit of experimenting, I found that some button head screws I had stopped perfectly at the 5mm halfway mark. So I put one on each side with nuts underneath to secure them in place.