I was under the impression that blow off valves were only there to compensate for too much boost when the car isn't under a heavy, or full throttle condition... helps not to break stuff, and helps to not lean out the engine too much during shifts... If the B2K cars run fine without them, then there is no point that i can see.. They don't add boost or create more power.
If I understand correctly, they relieve all the boost when the gas is let off. Helps relieve internal stress on the engine. I kinda think they sound neat, I don't wanna be rice but they are functional and b2ks are fast so.......
If you're accelerating and you release the throttle, the fully spooled up turbo effectively is now pumping against a closed path. No where to flow and the turbo becomes somewhat stalled. If a blowoff valve is added, this allows the turbo to spin on it's own accord.
Adding them to a Callaway? Man, that's gonna require some fabrication! Most of the turbo plumbing in the Callaways is hard tubing joined with sleeves and clamps. If I had to do it? I would pull the intercoolers and install it on the vertical inlet pipe to the intercooler adjacent to the valve covers. There seems to be a good 4-5" there for some gizmo or another.
Ive seen that pic before, but can't seem to locate it on their site anymore. Never noticed the BOV. Those are some impressive numbers....get your a/f ratio figured out and :crazy that thing will be crazy!!!!!