I'm doing some preemptive shopping. There was a lot of vibration @ ~1200 rpm, so I'm fairly certain that I will have to fix the motor mounts once my new toy is delivered.

I've searched the DIYs and the recommended fix is to fill the mounts with 60-80 shore PU. However, PU is not as nearly temperature resistant as silicone, in fact recommended operating temperature is below 180F. I'm assuming that the mechanical properties are similar.

I've used the search function, but didn't find anything relevant using 'silicone' as a keyword. Maybe I missed something?

Cost appears to be roughly the same:

Mold Max® 60 Higher Heat Resistant Silicone | Mold Making and Casting Materials Rubber, Plastic, Lifecasting, and More

 

I noticed that you used the word assume. I think that's gonna be important.

 

I meant that they are both 'bouncy'.

According to the following spec sheet PU has a 3x higher tensile and abrasive strengths but only until 70C, whereas silicone is good until 200C. Might be the better choice for turbo'd engines, if one can find a grade that has higher shore than 60.

http://www.misumiusa.com/CategoryIma...483.pdf‎

Amazing what a little bit more research turned up:

How To: DIY filled motor mounts [Archive] - Mazdas247