is stage 3 or better, with a UD pulley on it all that time, I'm with Ash. Like Ash I would rather be safe than SORRY. I love my Z way too much to take that risk for a few horsepower, when in actuality, you can gain more hosrepower with a lightened flywheel. You lose many more lbs there than with the pulley. Just my feelings. And, this is good info for everyone to make there own choice. Paul