byeatts, Normally whats happening when bored out an extra 1mm, or .5mm on the exhaust side with the exhaust port slopping down, so when bored the exhaust port is being lowered, which will better suite higher elevation riders giving you the sensation of more grunt as you call it. But its minimal. Most so called engine builders selling the 860 or 880 wont touch it and send it off to be replated. Talking to the replating companies, alot of these guys are just sending the cylinders to these replate companies and they are boring them out and replating them with no porting at all! So the end buyer gets a very poor 860 or 880. Then they get on the internet and say how good it runs or doesn't. If only they could try a real ported 860. It would surprise them.
At Terra Alps we do exhaust port changes for high elevation riders, or turbo applications, something no one else does. With lots of porting in other areas. Also our head design which you have makes good power and acceleration.
Ive been running the 880.s since 07,And also run Arts head which has been the same as yours. What I was suggesting is same extreme ported 860 cylinder bored to a 880 and as I indicated I adjusted the port height develops more hp by a good margin over my 860,s.On a fully modded motor with bored carbs instantly over-Reved and added 2 grams pin weight.Im Not belittling your 860 just adding some info, The 880 will not shine without bored carbs as theres an Air- flow bottleneck which holds it back with stock carbs.
