The EVO is one of my most favorite HD motors . It took me 2 yrs to figure out why , in a solid mounted frame the motor vibrated . I had bought a 1998 Heritage Springer and the vibration was excessive . Everyone said it was the flywheels . That Harley didn't do a great job balancing them . I was told to add a " harmonic " balancer to the flywheel and that would solve the problem . That to me was " treating the effect " and not treating the cause . Further research told me that Harley matched the pistons in weight to within 5 grams . That to some sounds great but to me , it was not tolerable . I tore down the motor and bought a set of KB (Keith Black ) racing pistons . They were matched in weight to within 1/2 gram , big difference . THAT ! ! ! solved the problem . It was very very smooth bike to ride . I later used JE Pistons and even liked them a little better . Those pistons come in std compression ( 9-1 ) and the high compression was (10.25-1) if I remember correctly . I rebuilt 6 evo's with complete success using the new pistons , some std compression and several with the high compression pistons . You can't believe the difference it makes till you try it . Regards Paul