Check the wiki spredsheet.
I think you have to mill the head after the pipe is on, mine lost ALL bottom end, but ripped from 14-37,39 mph. I mean ripped.
This one had the best hill climbing torque and off the line speed of all my peds. I couldn't live with it.
I took it off untill I find a FZ50 carb and then I will mill the head like .005", and put it back on.