Originally Posted by Ridin' Green
You obviously don't have a lot (if any) of time on two identical machines, one with the FX850 and one with the FX921. On two different models of one line, or different brands I can see some feeling that there's a bigger difference than there really is.
I have run both on the same exact machine with everything other than the model number and engine being identical for an entire fall season on both, doing both mowing and then heavy fall leaves with the deck in mulching mode. There is a difference, but it isn't that great. The 921 I used was averaging 1.8 gph in mulch mode doing heavy oak leaves which surprised me a little after everything i had read about how bad it would be.
That's great, maybe we can get a few more to chime in on power difference and fuel usage between these two engines.