Bad Vibrations

I just did a b18a1 swap into my 89 hatch and when we start the car it will vibrate. It isnt very bad at idle (750 rpm) but if i rev it even the slightes bit it gets really bad. We drove it around the block and the vibrations stayed consistant, but as soon as you hit a certain speed or RPM, the vibration would almost go away. i'm not too sure how high of rpms, but i'd say about 5000. What could be causing this problem? any help you could give me would be great.

it could be the harmonic balancer. try turning on the car, and see if you can see where the vibrations are comming from. if you have a chance, get a long screw driver, put the metal tip on the engine, and the oppisite end on your ear. follow the vibration untill you find whats causing it. if its comming from the bottom end, im willing to bet you its your harmonic balancer

My car did that and it was my frount motor mount sounds stupid but that what it was.I changed them all tho with siold ones runs great now...

Both sound like wise ideas to try for your car.