I've been fighting this problem for a while. I'll start from the top.

The engine warms up in the morning and you can feel the engine vibrate through the floor and anything attached (seats, dash, ect.). Around 3 grand it gets to stirring your insides. I've basically narrowed it down to two possibilites. Balancer or motor mounts. I'm getting a new balancer (on order) because it's not a bad thing to have new anyway. The vibration is not so much there in gear, clutch in or neutral doens't affect it. The engine runs smooth (a little bumpy at idle because of the cam) you can't see the engine moving from the engine comparment it will "buck" to the pass. side a bit under fast throttle but other than that it runs very smooth and doesn't move which confuses my on why I can feel it inside of the car. I've never had a broken/stretched mount nor a bad balancer. If anyone could spread some insight please respond. Thanks!.

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1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 WS6 Trans Am T-top car
4-bolt main 350, headers, Holley 650, T-5 and 3.23's.
Daily driver and restoration
13.98 @ 101

 

Every engine bucks a little to one side when accelerating, that's just normal from the torque. However if it lifts up than slams back down with a noticeable "THUD" when accelrating, then it's an engine mount.

Rough engines can be caused by so many things I'm not even going to suggest anything beyond that. heh Let the people who know what they're talking about help you.


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89 iroc-z 305 tbi
everything stock, except for a mirror that fell off

 

I threw the harmonic balancer off the rubber stripping and through the timing chain cover. So it is a big possibility

 

If your headers are tight to the side wall,
when the torque twists the engine against
the side wall, you can get a vibration at
some rpm, well that has happened to me
anyway.
Good luck
BenIroc
89 Iroc, TFS heads. Ford 9`` rear end, etc etc.