Why no underdrive pullies?

[01s281]

I have a 2001 saleen n/a and I am about to order a s-trim and I heard that you cant have underdrive pullies on the car. What exactly will I need to make this work. I called ford and they have like 5 ot 6 different pullies and I dont know which ones I will need. thanks

 

[ROADWARRIORSVT]

The underdriven crank pulley will slow down how fast your SCer spins, thus lowering the boost.

 

[01s281]

what about the water pump pulley? I heard that could get in the way.

 

[ROADWARRIORSVT]

I can't say,....I don't have underdrive pullies. I used my car in alot of stop-n-go traffic, so I did'nt want to underdrive any of the accessories.