ign. timing 340 vs. 416

It's not the stroke in and of itself, but the combination of the chamber, piston, fuel, and stroke that determines the best timing. A typical pump gas closed chamber 408 w/a quench dish will only require a max of about 32° and many like 28-30° total. A flat top piston, open iron chamber head, and pump gas, on that same engine, will want a little more, closer to 34°. A 340, with flat tops, open iron heads, and pump gas, may want as much as 38° total. Every car/package is different.