According to Hughes web sight, by changing lash, you can shorten duration anywhere from 5 to 20 degrees up to 4000rpm at which time they give full cam duration and lift per a regular hydraulic lifter. I'm happy with my combination ( engine and drive train ) right now except for my 60 foot times. I'm trying to move a very heavy car - over 4K. Wondering if these lifters with my existing cam would help.