Re: Can someone help explain the mechanics of proper flywheel weight
If one were to compare the weight of a flywheel next to the crankshaft itself, they would notice that the even the heaviest of flywheel is a drop in the bucket compared to the crankshaft. Remove the flywheel entirely, and the engine will still run just fine (once you figure a way to get it started!)
Go into a modern dyno lab and you'll see a bunch of engines hooked up to the load brake with noting more than a ~1 lbs Giubo joint. Less advanced, are all the hillbilly / ghetto engine run stands you see on YouTube that are running just-fine with nothing more that a puny flex plate.
So yeah, there is nothing "essential" about a flywheel. The only purpose they offer is a slight increase in rotational inertia to make clutch engagement a little easier for the driver. The harmonics of the crankshaft are handled by this little thing called the 'harmonic balancer' that bolts to the front of the crank.
In my personal experience, lightened flywheels are a lot of fun! It really changes the dynamics of the engine and makes it a lot more responsive to the driver. I have a ~550hp NA LS motor in a 2700 lbs mid engine Porsche. The engine has a 10 lbs flywheel and an UNSPRUNG clutch disc. The short of the story is that the engine needs to be kept above 2000 rpm whenever the car is moving. Below this rpm, that decrease in rotational inertia allows all the driveline lash to oscillate or "buck" in low torque applications. However, when I'm beating on it... hoo boy! She's a riot!
For a race car, go as light as you can go. You won't be disappointed. I've never heard anybody get out of a race and proclaim: "Man... I went too light with that flywheel. I really need to find a heavier flywheel!: