I have a killer 836 and I give most of the credit to the head work/porting. We had a debate some years ago on which attribute gave the biggest bang for the buck and most said displacement (from 736cc to 836cc), but all agreed it would be felt at the lower to mid-ranges. Everyone agreed that displacement would be a waste in the upper ranges without porting.
Somewhere is an old technical article from Jerry Branch (Branch Flow Works) and his findings and charts are accurate to this day. Unfortunately, the link to that no longer works. It shows that the exhaust ports hit a wall near the 7,000 rpm range. Cams, valves, pistons, carbs - nothing improved that flow until the ports were re-shaped and flow through the head improved.
I will caution you though, at rpms above 8,000 - you start taxing the factory supplied rod bolts. They become the weak link when rpm goes into the red. Buzz told me 10 times "it isn't about if, but when" you'll lose an engine to rod failure above 8,000 rpm. Now, he is a good salesman, but losing a complete engine - head and case with a thrown rod is bad - dropping 3 quarts of oil right in the path of my rear tire in the mountains is worse!
My build took two teardowns. The first was with the stock carbs and those did great - I mean up to 8,000 they were actually "better" in all respects than my CR29's. My bike was a monster when the tach got to 8,000 with the porting and stock carbs, but as it was coming alive - I was shutting it down in fear of losing a rod cap. The porting opened up so many of the other attributes - headers, cam, titanium valvetrain, 836 Wiseco, 10.5/1 compression, that those rods and their 14 lbs max-torque bolts became a nightmare. For the 2nd build (at 600 miles) APE studs top/bottom, Carrillo rods, and heavy-duty clutch springs went in there. That was 5 years ago and the bike still rips today. Porting must happen - too much testimony here and 1st hand experience not to do it. Don't try it yourself, bigger and smoother is not the goal - the flow and velocity have to increase. As you make that decision, you'll face big ports for max high-rpm filling that come alive at the peak of rpm or smaller ones for high volumetric filling earlier and huge gains in torque at highway speeds. That choice is up to you. Be sure that you match your components for the same delivery goals. A wild cam and big carbs don't work well on mild porting and vise-versa, if that big number is your goal, you'll need the big ports, the longer duration/lift cam and carbs to match.
Good luch with it. Just remember, it never ends
Gordon
