I have just fitted my own and what a difference. Love the sound it makes. Also replaced spark plugs, coil packs and replaced paper air filter with a RamAir foam filter.
One me strange thing I have noticed is that the flat spot has disappeared COMPLETELY!!! I have power all through the revs. Is this because it now breathes easier? Or a mixture of all above? I could also put money on it that it has more power now! Need to get it rolling road'ed to be certain.