[DavidNJ]

I used MathCad, which defaults to Joules. I change the units to lbf-ft, and it does the coversion. The quick part was assuming the flywheel clutch is a unitform disc, etc. I may have overcalculated the energy in the flywheel/clutch at idle...but not by an order of magnitude.

In Engine Analyzer Pro, the flywheel/clutch change could be worth 2-4 lb-ft² of inertia. That is worth maybe 5-7 lbf-ft of torque at 600 rpm/sec acceleration, or upto 9 hp at 6500. On no load situations, that is more dramatic, as Mike indicated.