Removing the secondary flies gives a significant boost to throttle response & torque.
I tried all the permutations. Ziptied, smaller, none & no flies & spindle.
The best throttle response was with no flies & removed spindle.
The mod requires a significant amount of fuel added at part & mid throttle openings. We did umpteen dyno runs in 06/07 to get it right.
It will not work without a pc3,V or bazzaz etc.
Anyone who says it isn't worth it is running the wrong fuelling map.