The construction of the filter is also another peice to the puzzle. Napa Gold filters uses the best elements in making of the filters. Pro select still has the same micron rating and flow ratio, but has less quality parts in it. The Nascar is a blend of both with the addition of the spinflow center tube. In my opinion the NG are the best, Nascar is the middle grade, and Proselect is the economy filter.
Bryan