Newbomb Turk said

Remember that these engines generally want less timing at peak torque and more timing at peak power.

How you get that done is the job.

If you know your engine peaks power at say 6k then you can reasonably figure peak torque is 1500-1800 rpm less than peak power.

So peak torque should be (in this example, yours could be different) in the 4200-4500 range.

Knowing that, you can now work to get the timing correct to peak torque. I’m not sure what heads you have or the particulars of your engine. You have to sort that out.

Having done this stuff for a bit I can say that unless you are turning 7500 plus your engine probably won’t need more than 35 total.

That means you should have 35 at 6k in my example.

I also know that it probably won’t want much more than 26-28 at peak torque.

Your job as the tuner is to figure out how to get the curve slow enough to get from say 20 initial at 1k idle to 26 by 4500.

Then you have to figure out how to get from 26 at 4500 to 35 at 6k.

It can be done but it’s easier if you have a distributor machine. And a day on a dyno would speed things up.

Also of note is the ignition you are using. Unless you are running points, every electronic ignition WILL retard with rpm.

Where it retards and how much is only a guess until you measure for it.

You have to account for this retard or you’ll never know what your actual timing is at any point in the rpm curve.

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Mattax said

Too bad someone messed with it.
The older Chrysler built DC and MP distributors came with very good curves in them for their specific purposes.
Both could be tweaked by adjusted the spring perches but all this seems to have been a secret (or been forgotten)
There should be a primary spring and a secondary spring. The primary spring has tension on it even when the distributor isn't spinning. The tension force determines the rpm when the advance weights will begin to move out.
The secondary spring engages when after the weights have moved the advance governer (slotted plate) X number of degrees.

The 'tach drive' units were set up for easy starting and winning drag races, stock eliminator type racing. A bit more initial tension will make a more consistant idle. Tach drive Race Distributor
The street/strip units (with vac advance) seem to get best idle with a close to factory high performance cam. Over 220 @ 50 duration the curve should be shifted a little so a higher initial is obtained for stability at idle.

Here's some examples of guys adjusting the curve on Chrysler built distributors.
Here as Rick as he works through and posts the effects of his changes
And an example of how that changes a bit with different combustion characteristics for later engine
I spill the beans on shaping the curve here

Earlier in that same thread are links to videos illustrating why the heavy secondary spring is important with electronic ignition.

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