ok, i agree with polarisrules, i have ZL 500 and it definetly likes the old go-go juice, but dont get me wrong the friggin' thiiing goes. i dont know SHlT all on MXZ 500, but i no that ZR/ZL 500 will anilate the 583! Arctic cat do make a slightly quiker engine then the XC 500 SP, i have prooven this with 2 different XC's.
thats my 2 pennies