I have a 3.8l from a 1975 Skyhawk that doesn't seem to be running right. There is a vibration that is noticable from the interior that varies directly with engine speed, whether the car is moving or not. It almost seems like there is something out of balance with the engine. This is the first time that I have ever driven a car with this engine, and I know that they may tend to shake, which is why Buick switched to the even fire design. While I know that there are a lot of variables involved (i.e. motor mounts, flywheel, clutch, etc.), I was hoping to hear some feedback from anybody who is familiar with the running characteristics of these engines. Is there a big difference in the running smoothness between the odd fire and even fire engines of the late 70's? I also have and even fire engine and am considering swapping the engines if I think it is worth the effort. Any feedback would be greatly appreciated.

Thanks,
Dan

I do have some experience with this kind of car (oldsmobile Starfire) so I'll trow in my .02 cents.
try to define WHEN it shakes the most and if and when this stops.
shaking on startup and idle? stops at about 2000-2500 rpm?
first the motormounts have always been a troublespot on these cars.
second make sure every normal item is in perfect order, I had a mild shaking engine once and the simple replacement of the sparkplug cables cured it.