with a 408 W using pistons that weigh 415 g
Source at 6500 rpm, 4" stroke and a 6.25" rod
Your Inertia Force is 2,193.65 pounds.
Your Stroke/Rod Ratio is 0.32 .
Effect of Rod/Stroke on TDC and BDC inertia force:
Your Upward Inertia Force at TDC is 2,895.62 pounds.
Your Downward Inertia Force at BDC is 1,491.68 pounds.
at 7000 rpms
Your Inertia Force is 2,544.11 pounds.
Your Stroke/Rod Ratio is 0.32 .
Effect of Rod/Stroke on TDC and BDC inertia force:
Your Upward Inertia Force at TDC is 3,358.23 pounds.
Your Downward Inertia Force at BDC is 1,730.00 pounds.
Those weights are per cylinder Imagine how much stress eight of those are going to put on the block and the entire bottom end.