With the F-Z you'll get less CFM but more MPH than with the F13. It all comes down to the housing and discharge size. We couldn't use the HDPE housing with the Z-Force because of being propelled by a ZTR. If the end user smashed the housing at high speed into a low hanging limb or something similar and caused the housing and impeller to fail while operational the ZTR operator could be injured by the resulting failure. In short we gave up some performance for safety. Get a demo of the F-Z to see what you think for yourself if interested.