For an Auto-trans car;
The first time the engine cares about it's Power-Timing is at stall. Below stall, it doesn't much matter what the timing is, so long as it idles nicely, takes throttle nicely, and doesn't bang into gear too harshly. The tune I outlined, will accomplish that.
to get the missing timing back at Part-Throttle, you use the Vcan.
However, in most cases the Sparkport is really too far up the bore for a cammed up stock-Scr engine, and vacuum advance will not be available until close to stall-speed. This often makes throttle-response from idle to stall, a lil sluggish. The only proper cure for that, that I know of, is more cylinder pressure, or more stall-timing.
The problem with getting more stall-timing, is that usually, it requires more initial-timing...... which will increase the idle-speed, which you will reduce with the speed screw, which will then upset youn T-slot sync, and usually, the trans bangs into gear, and with a low-stall convertor, the engone may pull against the brakes;
Therefor, IMO, you don't want to do that..... lol.
If more cylinder pressure is not an option, there is one trick that I have used, namely, a two-stage timing curve. But it's pretty tricky to set up, and if the stall is too low, the engine could get into detonation. If you solve that with a higher-octane gas, well, you shouldda just set the engine up with more cylinder pressure in the first place, cuz running best gas all the time, is gonna quickly gobble up all the money you didn't spend on doing that in the first place..........
The two-stage curve can help to solve the sluggish throttle response, so I use it as much as possible. I don't have a distributor machine, so it's a trial and error thing for me; but is so worth it, even if it takes all summer.
However, if you try it with the V-can, remember that the can starts dropping advance very quickly once the load begins increasing, which may or may not be a big deal, depending on the combo...........
Here's a hypothetical case;
Say you had a 2800 stall TC, and a 22* Vcan with Power-Timing of 28* at 2800. Together, at no load, that totals up to 50* at 2800, but the load is just going to the Tc, at which time, the engine, to stay out of detonation, only wants the 28*, so in this case, the Vcan has to be fully dropped out at 2800WOT.
But lets say, you are just cruising around at Part Throttle/2800/ and with the full 50* total. I guarantee that, as long as the engine stays out of detonation, you will be able to control the torque with the gas-pedal, and the timing will vary automatically from 50 to 28, seemlessy, which, working in tandem with the power-valve, and the vacuum secondaries (AVS, whatever) will be so stinking much fun, that you will want to be right there as much as possible.
Now just gear the car to make that happen at a comfortable speed, and you will be one happy camper!
Oh sorry;
2800 in Second gear will take 4.88s to get the speed to be ~30 mph, lol .
In First gear, 2800 with 2.94s , will get you the same ~ 30 mph.
The engine doesn't care how it has to pull from 30 mph @ 2800, with gearing; it will perform just the same either way. (4.88 x 1.45 = 7.08, and 2.94 x 2.45= 7.20)
However, getting to that 30 mph with 2.94s might be a whole nuther story compared to 4.88s ..................... lol. (If you need some 4.88s call me, lol.)
Between these two extremes are 3.91s, which will get you 2800 @ Part Throttle at; ~22mph in First, and ~38 in Second. Meh ...........
So much for hypotheticals, lol.