There are several different designs of Sanden compressors. Some Sandens have five or seven pistons. The number of pistons and cfm ratings are hidden in the part numbers on the air compressor. For example, model number SD709 is a 7-piston, 9-cfm compressor. The larger the cfm, the better that compressor will move air. Truly, the one you’ve got is probably the best as long as it is not locked up. Don’t bother wasting your time scrounging for a cfm or two. The other differences are external and have to do with how the A/C lines attach to the compressor.