so i have installed bbk underdrive pulleys on my 2004 mustang. Well im wondering if i need to install the stock harmonic on there now, or do i need to pitch them and get steeda hahaha.
My 03 has Summit Racing pulleys. I ditched the stock harmonic balancer and it runs fine...The BBK set comes with the water pump pulley, alternator pulley, and crank pulley. So you won't need the stock pulleys.
I have BBK on my '98 and the instructions say to install the balancer on the under drive crank pulley. It is a tight fit and I would double check the length of the replacement crank bolt - mine was not long enough to make up for the lost length so I bought another grade 8 bolt and used it. You can reuse yours - just inspect the balancer itself and make sure it is not coming apart where the elastomer is.