I have a s5 n/a block and I would like to bolt on a s4 tII transmission. I've been looking into buying a flywheel and clutch kit but most flywheels list that there are two counterweight. How are the counterweights different? Are the counterweights different because the rotors are lighter in the s5?

 

Yes, the counterweights are different from S4 to S5 due to the different rotor weights.
To use the TII tranny on the S5 N/A block, just get a flywheel and clutch combo for an S5 TII and you'll be good to go.

 

If you have an S5 engine, use the S5 counterweight off an auto S5 tranny.

 

Remember If you are Bolting up an S5 N/A to an S4 TII transmission,you are going to need(in your case),a S5 counterweight,an S5 Turbo lightened flywheel(aftermarket flywheel needs to be for a turbo engine),the TII Starter,the TII slave(for the Clutch)..then you will have to Figure out HOW to connect that to the Rest of the Driveline.If you are going to Remain N/A at the Differential then you need to get a Driveshaft converted so you can hook your TII Transmission to an N/A Differential..or do the "better thing"(if you go all out later on)you can just swap out the Rest of the Driveline,and put in a TII driveshaft,a TII differential and TIII half shafts.Anyhow.Some Info for ya.Good luck.