Re: bad vibration
good point rocket 50!
a basic cyclinder balance test will tell you right away if its a mechanical problem, if everything checks there I would look at engine balance (clutch problem, balancer bad, flywheel out of spec.)
you can do this two ways, either from the computer via Koer and hit the throttle quickly OW, or the old fashioned and my favorite, a pair of insulated plyers and a tachometer record the drop in rpms as you disconnect each cylinder, the lowest drop is your strongest cylinder. a bad cylinder will have nearly no drop at all.
93 mustang notch
~450hp 331 stroker - Sold