[quote=Fbody69]I had solid mounts on my 79 TA and you can feel the difference. It feels just like you have something up against the body that shouldn't be.... you get more vibration from the engine. The body mounts do serve a purpose quite well. That is, if you haven't eliminated them with solid mounts..... It's really easy to picture what they do. And what they can't do if they are solid. The bottom line is; Expect some extra vibration with solid body mounts.
Common sense tells you the polygraphite will absorb vibration better than solid metal... If you choose to ignore the common sense of it then look at the manufacturer material related specs and see that the material is much more 'insolating' than solid metal. The manufacturers all state it clearly.... If you have a scientific mind you can do a little digging and find the difference between solid polyurethane and solid metal. Very big difference in properties....
I've talked to (and my personal experience) is quite the opposite with solid mounts. Plus, when things like mounts are designed they are designed to absorb vibrations of a particular amplitude and frequency. Once you change the material from rubber to poly you affect the frequency range for the damping. So it doesn't work the same as saying "well it's softer therefore you get a little more damping."
If you have a problem with solid mounts either you need to get better engine mounts (if it's engine related) or better shocks (if it's road input related). Those are the things that should be doing the damping, not your subframe.
The type of polygraphite that was formulated to make subframe mounts was designed to absorb the same vibrations that the original rubber was. The only difference is less 'flex'. It's the 'perfect mount'. Just as solid as solid mounts but with the dampening capibility.... My 79 TA that had the solid mounts, and extra vibration due to them, was a frame off restore with attention paid to detail. The only mistake made was the solid mounts. The new owner agreed and has already switched them back to polygraphite style 'dampening' mount with great results. The odd vibration is now gone.
I'd love to see the data that shows these mounts of different material absorb the sample frequency range amplitude levels.
As for switching between the two, there are plenty of studies where some participants that received the placebo pills (sugar pills) instead of the real medicine somehow still noted an improvement.
If you look at the link I posted earlier there are plenty of people running solids (on 2nd Gens even) without this affect.
Common sense tells you the polygraphite will absorb vibration better than solid metal... If you choose to ignore the common sense of it then look at the manufacturer material related specs and see that the material is much more 'insolating' than solid metal. The manufacturers all state it clearly.... If you have a scientific mind you can do a little digging and find the difference between solid polyurethane and solid metal. Very big [/quote]
And what you are failing to understand is damping characteristics related to frequency range. Just because something is squishy or squishier does not mean it will damping in the same frequency range. This applies to vibration as well as well as noise and hydraulics. Some frequencies are not felt by the driver. Sometimes the solution is not to necessarily dampen all vibrations, noise, or hydraulics, but rather to move them outside of the range where the driver or system is affected by it. Ergo squisher is not always better.
Common sense would have us believe two coins (one twice the weight of the other) would not reach the ground when dropped at the same height. But wind resistance aside, we learned in grade school that gravity ultimately determines the acceleration of the coins and therefore they would land at the same time.
The bottom line is; Expect some extra vibration with solid body mounts. 
