Crankshaft pulley

[acrbill]

Besides that rubber ring that I have seen on a few stock pulleys, the actual cast iron plays some part in absorbing high frequency vibration. On the 1st gen Neon there was this huge cast iron block at the attachment point for the front motor mount. Its called a mass damper. Its there to absorb high frequency vibration that would eventually lead to metal fatigue at the attchment point for the FMM.

Don't get me wrong. I had an underdrive pulley on my Neon for over 50k miles.
It served me well. I am all for weight reduction anyway I can get it. I just don't buy the supposed HP gains.

I am far from an expert so take everything I say with a grain of salt.