Hey I know this has probably been covered before but I haven't found the information I need as yet. I have tried searching it....

I am getting a lightened flywheel for my S4 running a S4 13BT motor and 5 speed box, I understand from searching these forums that I need to get a auto S4 counter weight to bolt onto my lightened flywheel and balance the rotating assembly. I have been told that getting any other rear counterweight like a Rx8 one will put the balance out is this right?

I have also been advised by my Mazda dealer that I also need to weigh the total assembly of flywheel and rear counterweight and then machine the front counter weight to match... This doesn't sound right to me as the total weight of the flywheel won't effect the balance (as it itself should be balanced) it will however effect the inertia of the whole system. It is just the front and rear counter weights, rotors and eccentric shaft that will affect the balance right? So if I have the right rear counter weight to match my front one (eg a S4 one) I will be fine right?

 

Everything you need to know about rear counterweights can be found here:

http://www.mazdatrix.com/FAQ/RCOUNTERWEIGHTS.HTM

In short, your understandings are correct.