The Ultra series is an Aluminum Body carburetor, around 4 1/2 pounds lighter than a comparable standard construction type Holley.

Here is a review article about the Ultra:

http://www.dragzine.com/news/new-products/tech-review-holleys-new-ultra-series-carburetors/

Here is "The Ultimate Guide to Holley Carburetors" by Hotrod Magazine:

http://www.hotrod.com/how-to/engine/ccrp-0807-holley-carburetors-basics-guide/

The Dominator series was Originally designed for NASCAR but has been used everywhere.