I have read alot about this and watched the vids numerous times. It is a cool bit of engineering that was worked out to do this but I have never read any true tech results about gains. H.P., torque, top end speeds, 1/4 miles gains??? I have a bunch of XSs that I play with and they are pretty much in all different froms of builds. I love the sound and the torque is awesome but they are not what I consider a performance motor by any means. They are reliable, easy to work on, the best parts and tech support of any classic motor you will find. I just don't get why some choose to put big money into trying to make these into performance machines? I do just the opposite. I try to keep them as stock as possible, maybe a bore job on the standard sleeves to clean them up, clean the ports but thats about all. They run great when you get the ignition and carbs set up perfect. Most I see are'nt even close in that department and they are chasing power in all the wrong places. Unless you have lots of cash and time I feel that the XS is best at what it does stock and if you want a motor that likes to scream, smooth, and has lots of room for performance gains try building up an older inline 4. Some 550 inlines 4s I built would run circles around worked XSs with half the expense. I am not knocking the XS, just want to let those who have not done certain mods not feel like they are obliged too or missing something. Get your motor running as close to production new and you will have a great bike. Then pick on another to turn into your drag bike or road race project if you really want to tear it up. My next build is going to be a vintage road racer but I will again stay with a stock motor but get it running as new and know that basic service with easily gotten parts and techniques will give me miles of enjoyment with little money out of pocket. Less wrenching, more riding!