There are lots of data, including SAE Papers that show that in addition to dampening harmonics, the proper harmonic dampener will help the engine produce more horsepower.
http://www.atiracing.com/products/dampers/sae.htm
http://www.atiracing.com/products/dampers/sae.htm
There is a great SAE Paper regarding harmonic balancers and its effects in horsepower.
https://www.sae.org/publications/tec...ontent/790763/