[aeroace]

Everything said so-far is pretty much true. I used to snap rubber motor mounts every other week on my own car. I drilled them and put a bolt and two fender washers thru them (had to shave down the bolt head and other side too to clear the block). that helped. Never bought urethane, but the rubber was breaking not just flexing. Used solid moroso's for four years seemed great, but everything started to rattle eventually.

The best way to prevent motor torque-over is to install an aluminum flywheel. The 300 lb/ft cobras with steel flywheels often had chewed-up sidepipe exit holes. The 530 lb/ft cobras with alum. flywheels didn't. The lower rotational inertia of the flywheel, the less it resists being turned, thus your motor doesn't torque over onder hard throttle, or downshifts. The 560 lb/ft cobras do kiss the exit on a SPF, with rubber mounts and an alum. fly. Urethanes, or a solid on the drivers side, and rubber on the other may cure, didn't try.

The explanation was based on the results, not conjecture.