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Originally Posted by DavidNJ
My quick calc says the energy stored in a 45# flywheel clutch assembly at idle is about twice as much as a 2800# car (with driver) moving 5mph. Going from a 45# 11" assembly to a 18# 8.5" assembly will drop the stored energy by over 75%.
Yes, if you have 700gm pistons and 900gm rods with a 60# crank, you will still have quite a lump. However if you have 400gm pistons with 520gm rods and a 40# crank, it will be significant.
BTW, do you have a formula for calculating the inertia of the pistons and the rods?
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I may of course be wrong but I think that your quick calc is WAY out. Did you perhaps forget to convert the units? If you use rpm,inches and lbs to calculate the flywheel stored energy then the speed (5mph) needs converting to inches/minute.
The 'guesstimate' that I included in mine was to assume that a 40 lbs flywheel represents about half of the total rotating mass. I don't know how true that is.
I don't have a formula for piston inertia, I made the assumption that it is fairly neutral because they spend an equal amount of time accelerating and decelerating.