Hello all. I have scoured the search function but am still having trouble.
I installed my new 406sbc last week in my '69 and I have been struggling to to find an engine vibration in the 1000-1100rpm range. Anything below or above this range(up to 4k) smooths out pretty good but for that 100rpm range it shakes the whole dash and steering wheel pretty bad. (It makes idling down the street pretty embarrassing)
Prior to assembly, I had the rotating assembly balanced (external balance) at a highly reputable machine shop and I have already eliminated the drivetrain as the culprit by observing the same vibration with the torque converter disconnected from the flywheel. (Happens in Park, Neutral)
I have tried adjusting the timing and I am currently running total advance @38 (14 initial + 24 mech) all-in at 3000rpm. I am pulling good vacuum at 17" idle (~800rpm) so I do not suspect a vacuum leak. The engine runs and sounds great but the plugs read a little lean(White, no brown). I am using energy suspension poly engine mounts and admit that the engine sits slightly higher in the frame mount groove on the passenger side; but would this make that much of a difference?
Any ideas would be greatly appreciated.
406sbc (10.8:1 compression)
Scat 9000 ext balance crank
5.7" Scat forged rods "stroker clearanced" (yeah right)
Externally balanced (8" balancer, sfi 168 tooth flexplate)
Comp Cams Hyd Roller 280HR (280 dur, 224 @.050, .525 i/e, 110 lobe ctr)
Edelbrock Performer EPS intake (2701)
Edelbrock Performer RPM heads 170cc, 70cc (60719)
Edelbrock Performer 750cfm Carb (1411)