Here's something to think about. Actual Racepak data collected from my personal 2525lb driver/car, with some rough calculations applied. Sbc power, but exact same car/trans/flywheel/clutch/gearing/tires. Exact same heads/intake/carb/cam/compression. Only difference between these two engines was the rotating assy...
Scat cast crank (49lbs), steel rods, 1863g bobweight, WOT no-load rev rate of 8500rev/sec.
In 3rd gear @ 535rev/sec accel rate, 31.47ftlbs absorbed by the rotating assy, 468.53ftlbs twisting the transmission's input shaft.
In 1st gear @ 1975rev/sec accel rate, 116.18ftllbs absorbed by the rotating assy, 383.82ftlbs twisting the transmission's input shaft.
Scat F43 lightweight crank (42.1lbs), aluminum rods, 1492g bobweight, WOT no-load rev rate of 11,515rev/sec.
In 3rd gear @ 541rev/sec accel rate, 23.49ftlbs absorbed by the rotating assy, 476.51ftlbs twisting the transmission's input shaft.
In 1st gear @ 2217rev/sec accel rate, 96.27ftllbs absorbed by the rotating assy, 403.73ftlbs twisting the transmission's input shaft.
Comparing the two...
...both engines put out the same torque when operating steady state @ 5000rpm.
...WOT 4500-5500 at 3rd gear acceleration rate, the lightweight rotating assy hits the transmission's input shaft with about 7.98ftlbs more torque.
...WOT 4500-5500 at 1st gear acceleration rate, the lightweight rotating assy hits the transmission's input shaft with about 19.91ftlbs more torque.
The difference in bobweight was about 3.27lbs, crankshaft weight difference about 6.9lbs. Flywheel/clutch weight is typically centered farther from the axis of rotation than the crankshaft, making it an even more effective place to lose weight.
Grant