As said, the adjuster is just to delay the onset . The thing that controls how much, is the stops on the arms. The number on the arm tells you in cam degrees how much timing the device is capable of giving; you double it to see it at the crank. If your arm has a 9 on it, that would be 18*at the crank. The arm also has a letter on it; either an R or an L. This refers to in what direction the device is to be installed, SBMs are "R", IIRC, and everything else is "L". Cans for points are different from cans for Mopar Electronics.
You can grind as much off the stops as you dare and I have seen 24* become available.
As to tuning them that's easy.
Put a vacuum gauge on the sparkport, then rev your engine up until the vacuum peaks. Lower the Rs until you find the lowest rpm with that highest vacuum. Ima guessing you will hit it at ~1800rpm.
With the Vcan disconnected;
Rev it up until you get back to that rpm (1800 in my example), and set it on the fast idle cam. Then crank in more timing. just crank the D no timing lite. The rpm will rise, so reduce it back to the starting point. Then crank in more timing, repeat until the rpm no longer rises. With the Rpm back at the starting point, put the timing light on it, and take out 3 degrees. My guess is it will be over 40 but less than 50. Write it down.Write it down.Write it down.
Put the timing back to the pre-test value, and idle the engine back to normal.
You now have the ideal no-load timing for the test rpm, with a 3* comfort zone.
Lets say it was 1800rpm, and lets say you have 3.23 gears and 27" tires. And let's say the engine liked 44*. With an automatic, you now have very close to ideal cruise timing at; 18mph in first gear; 30 mph in second; and 44 in drive.
Now repeat the test every 300 to 400rpm until you hit 3000.
Plot all your numbers on a graph, and connect the dots..
Now reset your power-timing to 34* all in/ no Vcan timing.. Rev it to 4000 and make sure the curve is done; then,back to idle.
New scrap of paper; record your timing every 400 rpm starting at 1000 rpm and ending at wherever your D stopped advancing or 4000 whichever is more. Plot your numbers on the SAME graph as before, and connect the dots. Run rpm across the bottom from zero on the left to 4000 on the right. And plot advance every 2* up the left from zero to at least 56*, 60 is better.
Ok so , now you have two curves on that graph; one is "WOT timing" and the other is "cruise timing" and now you just gotta marry them with the Vcan, as best as you can.
Here are some of my Observations;
#1, The Vcan is NOT strictly for mpgs. The V-can supplys ALL your timing needs Except at WOT.
Without a V-can, your engine will NEVER have correct timing, at anything but maybe, I say maybe; at WOT. That's it. I'd be willing to guess that, time-wise, 98% of your engine's life will never be at WOT; so why in the world would anyone ever run a streeter without a Vcan, IDK.
#2, if you have an automatic with a whatever stall, say 2400. Then you don't much care what the timing is below 2400, unless it causes pinging.
#3, it is impossible without computer controlled timing, to ever have proper timing, except three times; #1 at WOT after 3600, #2 at idle, and #3 at exactly one time in the cruise mode,maybe; if you put it there.
#4, Because the vast majority of the time that your engine is running, it will NOT be at WOT, it is always better to sacrifice Power-timing, to get Part Throttle or Cruise timing, as long as it does not cause detonation.
#5, because only a small percentage of time will the engine be at idle, and it is never (with an automatic) required to pull from idle; it is always better to sacrifice Idle-Timing to get closer to best Part-Throttle Timing.
#6, the closer you get your Vcan working to ideally all the time, the more fun that engine will be.
Ok back to your graphs; How much timing is your current Vcan able to command? Lets say it is 16*. Go to your cruise graph and subtract 16* or whatever your Vcan is able, from every cruise plot, and connect the dots.
The difference from the New Plot to the Power-Timing Line is what you have to correct.
Sounds easy; but I bet it will take you two summers.lol.
