To get a bit more poke out of a standard 851, the Australian importer tested opening up the rather tight junction on the standard exhaust and improving air intake by replacing the standard airbox lid with just a frame to hold the filter in place. A new chip was made to suit by a local company here, and the improvement was about 8-10 hp from memory. In short, V twins need to breathe!! Be prepared to wear ear plugs as the indunction noise can get quite harsh. I rode the bikes on the dyno runs so take my word for it!. Hope this helps, Cheers...