I just got my prochamber and it came with a funnel shaped sleeve. What is this for and what side does this go on? How is this installed (the sleeve)?

 

My UPR came with a similar piece and it went inside the drivers side mid pipe where it bolts to the exhaust manifold

 

Exactly....Mac had a huge problem with the Prochamber not sealing up to the manifold so they started including a metal sleeve, which solved the problem. You might also look into replacing the passenger side exhaust manifold gasket also...check out this write up and you'll be good to go.

http://www.cardomain.com/ride/593952/3