http://forums.stangnet.com/showthread.php?t=613998
2 hp increase, not much... but its an increase.
And yes, it makes a bit of difference in tone.
I am on so many forums it will take some time to search them all
I will post what I find.
BUT... there wasnt a drop, and there was a slight power increase.
From the research I did quite a while back... The higher you twist it and the more power you make... the more beneficial the X becomes.
Jim