Flex plates
You have a DAMPER issue. Next up is the crank or the block.
The flex plate is telling you it’s pissed off.
Get a better damper.
Would the damper cause that so quickly ?
I’m not questioning your opinion,,,just curious.
I was thinking maybe wrong crank balance ?
Or something out of kilter ?
What about the balance for the stroker crank,,,,could it be wrong bobweight,,,and imbalance being masked by all the other things combined.
You know,,,noise and vibration from running down the track ?
Or,,,possibly a crank flange that is not true ?
I’m assuming that this was a complete fresh engine,,,,and the converter and transmission were used ?
Tommy