When the mechanical advance continues above cruise rpm, that's OK. Mechanical advance is to compensate for the increasing speed of the crank and pistons until the improvement in flame development is so good that it matches the increase in engine speed.
A torque converter's relationship to engine load is something I don't have a great understanding of. If we take the stall speed as brake speed, we can say its similar to letting the clutch fully engage. But we also know that stall speed varies with torque. Under light load the 2400 stall converter will be driving the transmission with only small loss at 1400 rpm, and on the other side if we put that same converter behind a more powerful engine and do a brake stall test, it will go to 2600 or 2800 rpm.
So from the above, I would have thought that torque converter had little to do with cruising loads.
However after I had T/A tighten up the torque converter for my Barracuda, the car had issues with pinging at cruise along with some dead spots at heavy part throttle.
Now it also happened to be that the mechanical timing was all in early with that distributor. When used with the vac advance, the pinging at cruise was always in this range.
It happened even at low speed (50-55 mph) flat terrain after an hour or two on the road. Was this due to just the distributor, or also due to the change in the converter?
I still don't know for sure. And since the was down for a year, did changes in reformulated fuel at that time play into the equation?
Below is a graph of the timing where it pinged with red highlighting the problem rpms.
It shown in relation to the timing that it now has with a different distributor.
View attachment 1715748989
The factory always had the timing continue advancing well above typical cruising rpm.
View attachment 1715748995
Max and min here are refernces to the advance curves. Base timing could be set higher or lower as fuel and altitude permitted. That would shift the timing curve up or down.
The exception was for drag race only, running with no vacuum advance.
But even in drag racing, the tach drive distributors are set up with one heavy long looped spring to allow a slight increase with rpm when used with a quick ECU.
My coworker had experimented with removing that spring (because that trick had worked with the dual point distributors) and after many disappointing runs had put it back in and started hitting their times again. However a large portion of that relates to the time lost in the electronic switching.
I mention the drag racing because almost certainly that is where the remove one spring, all in early, clearly started.
