>ok, so when we were talking about the FBO plate working against me, This is where I went off track.
The plate is used to limit the working range of the flyweights It is NOT needed on ALL distributors, but is useful perhaps in most factory ones. If your D has a working range of more than 18 or 20 degrees, then the plate can be a quick fix, to get it down to less than 18/20 which is often/usually a good thing. After the working range has been established,it should not be doing anything else. It is a useful tuning aid to help you meet your engines needs, without doing a bunch of welding and grinding.
is it because the vacuum advance can get the advance as high as it needs to be under light throttle with the plate?
Yes, the Vcan adds it's timing, as it is signaled to do, which could be at any time, from PT (PartThrottle) to perhaps 40/50% primary opening. But it does not begin until the vacuum is high enough to BEGIN bringing it in, which may not be until 1600rpm (an arbitrary number I pulled from a hat), or later . If you look into your passenger side primary bore you will see the advance port on the front somewhere, that is not mirrored on the drivers side.
On my Holley with my timing curve (14-idle/ 28*@2800), the Vcan brings 22* to the party, to cruise at 28+22=50*. But as I start to feed it throttle, the V-can timing starts to decrease. Somewhere just before the secondaries begin to open, the V-can timing has dropped to zero, and she is back to 28*@2800. From there the timing increases to a max of 32/34* all-in, in the range of 3200 to 3400. This is nice and safe, as to detonation, and makes plenty enough power for me, at 3200=38mph in second gear. Opening the secondaries gets me tirespin every time.
Im assuming thats why being the full advance under WOT is normally around 34-38 with a decent cam nd all..or am i totally wrong..?
Yes and no. 4 or 50 decades of testing has shown that HP MOPAR small blocks, on the dyno, like 34 to 38 degrees Power-Timing after about 3600rpm, depending of how efficient the chambers are.
But like I say, on the street you will never feel the difference of 3* less than perfection; but the engine will begin detonating with just 1* too much. Unabated detonation usually breaks stuff, so ALWAYS err on the safe side.
In other words, the FBO plate is not hurting anything UNLESS using the vacuum advance?
The plate should have nothing to do with the Vcan. They are separate and distinct, and each is tuned separately. The thing is this, in the life of your engine, maybe 1% of it is gonna be at WOT. The cast majority of time, time, the engine will be loafing along at less than 3600rpm. So, IMO, you wanna concentrate on getting your PT right, even if you have to sacrfice some sub-all-in timing (not PowerTiming) to get it. So if, to get the PT timing optimized, you have to delay the all-in rpm, or reduce the PowerTiming a couple of degrees, that's what I would do.
AND, if using the vacuum advance, you would want a spring tight enough to keep it from passing 34-38 total under WOT?
I guess yes. This is really two questions. Yes, the PowerTiming should fall in the zone of 32 to 38 depending on the efficiency of the chamber.
and this is achieved by the combination of flyweight mass and spring selection. BUT once again, the Vacuum Advance is a separate system and should not affect or be affected by the centrifugal system. One has nothing to do with the other.
