1BAD80 said:
You can call me "Hib"
For facts ask anyone that has them.
Or you could write VP&B for the data.
Ok...I guess I should establish credibility.
I've worked on and raced Corvettes for 35 years. I've worked on C1s, 2s, 3s, 4s and 5s and I currently work on C3, 4 and 5 on a regular basis. I own an maintain a C3 and a C4. I've been an automotive technical writer since 1984 and have done technical work for most of the Corvette magazines that circulate nationally. In the past, on a contract basis, I've done product developoment work for aftermarket companies. I'm a former service technician. I've got a degree in automotive service technology. I belong to the Society of Automotive Engineers. I've keep factory service manuals on file for 63, 65, 71 and 82-03. I've worked with polyeurthane suspension parts amost since the stuff was first introduced in the late 1970s. Generally my work has been with either Energy Suspension or Vette Brakes and Products. I've worked with urethane powertrain mounting pieces for about as long as they've been available. I don't need to write VB&P for information because I talk to their engineering people on the phone regularly.
Now...here are the facts.
1) Polyurethane has a much higher durometer than rubber, thus it's stiffer by a significant measure.
2) The purpose of flexible powertrain mounts is to damp engine noise and vibration. Use a powertrain mount material that is stiffer than rubber and more noise and vibration will transfer from the engine to the chassis and, then, to the interior because the stiffer material provides a lower level of damping.
3) Polyurethane is more durable than rubber but polyurethane powertrain mounts, as long as they are the "safety mount" design are no more reliable than rubber mounts because both designs use bonded construction where the rubber or urethane is bonded to the metal.
I was explaining what I had to USE ON MY CAR for motor mounts.
I have a little more than average horse power with a small block 427 motor, there is not that much vibration since the motor is balanced very well, its the torque of the motor that break's the motor mount's NOT the vibration, it only shakes the whole car because of the cam.
My C4 has a 460cuin BBC (535hp/530lbs/ft) with all the good stuff--forged crank, Crower rods, 9.75:1 BME pistons, Crane mechanical roller, ported/polished oval ports with L88 valves, roller rockers, Edelbrock performer, Holley 850, headers, MSD ign. and other go-fast stuff.
But...it uses stock GM rubber engine mounts. The car has well over 100 passes on it and they've yet to break. My engine, in spite of it's radical, roller cam does not shake the whole car because I have rubber engine mounts to damp a lot of shaking caused by the cam's rough idle.
Bottom line. Polyurethane engine mounts are more durable than rubber in many cases. Urethane powertrain mounts will reduce engine movement due to torque reaction or misfire and will transfer more of that movement to the chassis. There is no improvment in engine performance nor is there an improvement in the car's handling from installing polyurethane powertrain mounts. Iif you decide to install them, understand that there will be an increase in noise and vibration from the engine to the chassis and then to the interior.
