this by that great master mechanic aw. checked max rpm with doubles high lift gator comb. max at 3860. blades engaged . same check w high lifts only 3860.. surprised me a bit. by the way im talkin a 20 kohler command. another surprise max rpm without bldes engaged 3750. ??? also checked 141/2 briggs max rpm 3650 turned all the way up. engaged bld 3250. turned it back to 3350 which is what i started with unengaged. engaged 3250. now this leaves me knowing one thing for sure . that i dont understand all i know about these things guess the main result is that doubles didnt slow the rpm. of course it would have more affect in cut ,as u have a lot more blade contact with the grass. hope somebody finds this info worth while.