Depends on your Vcan, and when the 36 was in by; but I'm pretty sure the engine didn't like the total timing it was seeing, and you interpreted detonation as flutter.
For instance if the centrifugal begins advancing at 1000 and is all in by 2800, then it is advancing 21* in 1800 rpm, or 1.67degrees per 100rpm. Therefore at 1500, she would be seeing 15* plus 5x1.67 plus the can which could be as little as 9 or as much as 22. So that totals 32* to 45*at light throttle. By 2200 it looks like 15* plus 12x1.67 plus 9 to 22= 44* to 57*, at light throttle.
These numbers are probably too high for a stock iron headed engine
Bottom line is this; if you can change the severity of the flutter by changing the amount of throttle, or if it disappears with a defeated Vcan....... then the flutter was probably detonation.
And you want to avoid detonation at any cost, cuz detonation can break your pistons pretty quick.
It seems there are quite a few guys here on FABO, that are Gung-Ho to throw timing at every engine they come across. Here may be a prime example of what not to do.
The factory timings on a 69 383-2bbl automatic,The only FSM I have, were pretty aggressive. I see it at; 7.5 initial, and 2 to 12 at 1000,16 to 20 at 1500,34 to 38 at 4600, and with 21 to 27 in the Vcan by 13.5 inches vacuum. The 4bbl specs are a bit tamer
IMO, IMO,IMO, it is better to be 3 to 5 degrees retarded at all points, even 3 short at WOT, than even just 1 too many. On the street, at WOT, I can almost guarantee you,that your butt-dyno will not be able to measure perhaps even 3 degrees short of optimum.
So, again, IMO, don't be in a hurry to throw timing at it, a mistake can be very expensive. Sneak up on it.
