I installed the 20mm intake manifold. Doesn't appear to be much difference between manifolds, but carb side does get rid of step down between 20mm carb adapter and approx 17mm OEM manifold. I guess you could port match between the carb adapter and OEM manifold, but would weaken the manifold, just seemed easier to buy another part. The opening into the reed cage appeared to be the same size on both manifolds. I wasn't expecting much change in performance, but did compute approx 38% area increase between the opening of the 17mm OEM manifold and 20mm manifold.
I put it all back together and went for test ride. Was pleasantly surprised, engine ran noticeably better, actually ran pretty awesome. I think this is the 1st time I am starting to think I want to put BBK on Super 9 LC. Up until now, Super 9 LC was always better ride compared with People 50 2T with BBK. Although Super 9 LC doesn't have the great take-off BBK has, it was generally more fun to ride, had more consistent performance, better top speed, and no concern about overheating.
I guess the step between the 17mm OEM intake manifold and the 20mm intake adapter was doing something bad. After my before and after test today, I can highly recommend it, was worth the $'s and work to get it installed. Engine still runs hot, high CHT 418F, but cooler weather seems to be helping, and 20mm intake manifold seems to be going in the right direction too. Before 20mm intake manifold, max revs seemed to be approx 9600, today with 20mm intake manifold max revs was 10,080. so significant increase. I made no adjustments to carb, and it seemed to be about the same over rich tune, but just ran better.
I finally received Airsal gasket sets today, ordered 2 gaskets sets and one was correct, the other wrong, bummer. Anyway, since still running hot and carb is still tuned too rich to really rev out like it should, I will test lowering compression by installing an extra head gasket. Probably be a couple of weeks before I can get to it, but will report back test results after I make the change. Cheers