Engine acceleration rate plays a big part in the amount of engine torque that's available to do external work. In Tig's graph above, the engine flashes from 1850 to 6100 in .456sec. That's an average engine accel rate of 9320 rpm per second between 1850 and 6100.

My stick shift car's current engine has a no-load acceleration rate of 11,500 rpm per second. If you were to dyno that engine at its no-load 11,500 rpm accel rate thru the heart of it's torque curve, the dyno would show zero torque output. At that accel rate all the engine's torque output would be used internally to accelerate its rotating assy, with no torque left over to do any external work.

At a 9320 rpm per second accel rate like in the initial part of Tig's graph, about 81% of my engine's torque potential would get absorbed internally, with only about 19% of it's torque potential available to do external work. Say my engine makes 500ftlbs steady state, at a 9320rpm accel rate it would only have 19% or 95ftlbs left over to do external work.

WOT at a zero rpm acceleration rate, all of an engine's torque potential is available to do external work. Where Tig's graph knees over to a flat line at .456sec, that's the point where the engine's maximum torque output suddenly gets applied to his converter shell.

The points on his graph where the engine is getting pulled down against WOT after the shifts, that's where torque applied to the converter shell actually exceeds the engine's maximum torque output. That's because energy absorbed/stored within the engine's rotating assy as it gained rpm then gets discharged as the engine loses rpm. That discharge of stored inertia energy is what causes the tires to chirp on the street during a firm automatic shift.

Being a stick guy myself, I find it's easier to think of the converter itself as a self-contained load sensitive variable ratio transmission. The converter basically "converts" shell rpm hydraulically to increase torque applied to the slower spinning transmission input shaft.

Grant