Hello, everyone. I am having an issue with engine vibration in my big block duster and I am trying to find the cause. The specs are: -'77 400 big block bored .030" over with Keith Black hypereutectic pistons -9:1 compression -Summit 282/292 cam (224/234 @ .050) with .465/.488" lift and 114 lsa -Edelbrock Performer RPM intake manifold -Holley 750 vacuum secondary carb -Mopar performance ignition -windage tray -Harmonic balancer and torque converter/flexplate are stock I guess the vibration has been with me for a little while, but it got much worse when I put the new polyurethane trans mount in last week. I thought it was driveline at first, but it does it when the car is in park or neutral also. The vibration is present at all engine speeds, although it varies in intensity. It is particularly bad from about 1200 rpm to about 1800 rpm. I have checked my engine mounts and they are tight and not missing any bolts, and I took the accessory belt off to rule out the water pump and alternator and the vibration is still there. I also checked my ignition timing and the timing is still where I set it so the harmonic balancer does not appear to have slipped. Could it be the torque converter/flexplate? Or could the damper be faulty even though the timing marks have not moved? It feels like the time the water pump bearing went out on my truck, but like I said, it still does it when I remove the belt. Any thoughts? Is there any way to rule out either the torque converter or the harmonic balancer? Thanks!