88 TII Death Vibration
 

The Background:

Recently got my girlfriend an 88 TII with a blown motor. We rebuilt the motor with a mild street port and hybrid turbo. Finally got around to finishing it and started it up. Took it to my tuner for a break-in street tune. Fixed a few things and finished the BOV.
The motor is an s4 block with fd housings and s5 internals. All counter weights were changed to s5 as well. the only thing not factory is a light weight flywheel can't remember the brand but the same one I used on my FD. The car has brand new poly urethane mounts for the engine and trans.

Car Mods List:
S4 plates, S5 internals, S6 Housings. Lightweight Flywheel, ACT 6 puck
Engine has been studded.
Racing Beat Turbo Exhaust system
Hybrid Turbo to s5 turbo manifold.
Every thing is new on motor/car.
Red Poly Urethane Motor/Trans Mounts

The issue:

At low engine speeds the car seems to be rattling itself to death and never gets better through the rev range. Every 30 year old piece of plastic sounds and feels like it is going to collapse. You can not hear the car(exhaust, bov, tire noise) all you hear is chaos.

We pulled the front cover to make sure everything was set correctly, i checked the inspection panel to make sure the clutch was bolted on correctly. Has anyone ever had this issue?

I doubt it, but were the rotors within range letter wise? And i also thought flywheels were different between s5 and s6.........i could be very wrong on that

And is it all engine vibration? Or only going down the road?

Both rotors were the same weight came from a part out engine, as well as the counterweights. Everywhere I've looked states that s5 and s6 flywheels are interchangable as well as the rear counterweights.

The vibration happens in both free revving as well as driving, but is much worse while driving. I am planning on dropping the trans and bolting on a stock fd flywheel and rear counterweight and see if anything changes.