Looking for some input.
My project that I picked up a couple years ago has been great up until recently. The motor is a 383 with a scat crank, eagle rods, unknown pistons, unknown cam. factory vibration dampener. I don't hear any noises. I had excessive movement so I replaced the motor mounts and trans mount with poly from the factory rubber mounts. I took the car out and noticed a very noticeable vibration from 1500 to 5000, It feels like a miss almost, but checked the temp at the header at the head and they are within 2-3 degrees of each other. I can't hear a miss over the exhaust and supercharger. I checked the plugs and they are light gray little to no soot. I am running a terminator X with a dual sync distributor, I am wondering if the dual sync is my issue. When I had the car tuned last year, the tuner didn't say anything about a miss or excessive vibration, even earlier this year I didn't notice anything. I also used a stethoscope to listen to each injector and they all sound the same.

New within the last 2 years
New plugs and wires,
Holley dual sync distributor
Holley Terminator X
Tuned by a reputable shop
60lb injectors from southbay injectors

 

First thing to do would be to disconnect everything from the motor that's not the motor, to the greatest extent possible, and see if it's affected. All belts etc. specifically.