I'm posting this here in f.i. because this is where this info would probably be most applicable..
I've been playing around with my home fabbed motor mounts for the last 2 years, off and on, trying to get the best combination of vibration isolation and stiffness without wheelhop during shifts. I learned so much more than I ever thought I would, but that's another thread, another day. Right now all I want to share is my way of isolating vibration with the torque (front and back) mounts. What I did was take one 60a bushing, put that in one side of the mount, and then install another harder bushing on the other side, with the hole in the bushing enlarged so it does not contact the center metal sleeve until the motor torques it. (maybe about 1/8" gap.) So when cruising, idling, most driving, the single softer bushing isolates the motor vibration, but when shifting hard, etc, the harder bushing controls the movement. It seems to work really well, I'm actually rather proud of myself right now..

 

very interesting, i would worry about the bushing or bolt breaking from the impact though

 

Okay, think about this for a minute. Those companies that say you can only use 3 mounts, and warranty it that way, they have 2 bushings in each mount. Take one of those bushings out of the back mount, and put it in the front. Now each bushing has only half the force exerted on it, due to it having twice the effective leverage on the motor. So you could do that with 60a bushings. I'm doing it with those 2 + the 80a bushings.
So what I've done is actually significantly stronger than what the companies already sell and warranty. I'm basically just reinforcing the 60a bushings, while preserving them for vibration isolation. That's probably the best way to look at it..
Now if you decided to do this without using a front mount, (ie, half assed..), you could cause a problem if you enlarged the harder bushing hole too much, because then the softer mount could be compressed to its tearing point and the mount could bottom out internally before the harder bushing was able to stop the motion. But it would take more than the approx 1/8" gap I created to do that, so that potential problem is easily avoided.

 

good job. its kinda like progressive spring rates, softer at first to absorb bumps, then it gets stiffer the more you compress it.

 

Pretty much, yeah..