Hi John,
Congratulations on your results. Your doing very well to start racing and have consistent finishing. I raced for about 10 years in the NZCMRR 500 clubmans class first riding myself and then after a painful crash having someone else ride my bike. My first few years were terriable for non finishes but we sorted it in the end.
Going back to your original post.
I have no experience with BMW or your carbs and ignition type but for what its work here are my ideas.
Firstly you are in general correct - if you increase compression you should retard ignition. Paul Dunstal for example recomends coming back from about 30 deg to 28 degree advance when increasing CR to 10.5 plus in the 750 Norton. The best theoretical discussion together with lab results I have seen on the subject is in Gordon Blairs book Design and Simulation of Four Stroke Engines.
http://www.goodreads.com/book/show/4537 ... ke-engines
However this is a book for engineers and most definitely does NOT give a cook book answer to your question. He uses an engine test bed to investigate the burn time inside engines for various fuels and compressions.
In practice CR, head design, inlet tract efficency, mixture, plug location, fuel atomisation etc etc will all impact to determine the ultimate curve so theory is only going to help you to understand and direct your experiments ( unless you have accccess to some very serious computing and sofware programmes !!!)
A practical if expensive approach is to follow the methods described in G G Bells books. Run your engine on a brake dyno where you can control the load on the engine for incremental steps of rpm. At each point determine your best carb and ignition settings and then programme your ignition curve.
This is expensive but if you can get a brake dyno this is the way to do it. Unfortunatly getting a brake dyno at a viable price WITH AN OPERATOR WHO KNOWS WHAT THEY ARE DOING!! is almost impossible.
Viable alternatives.
-I have read about onboard data loggers. This might be good but I have no experience.
-Getting ignition right by reading spark plugs. Gordon Jennings wrote some excellent articles about reading spark plugs. For carburation AND timing.
Read this. This is very very very good!
http://www.strappe.com/plugs.html
Jennings says most riders have too much ignition advance , jet to rich on mains and have too cold a plug.
I do not feel qualified to comment on the heat range statement but based on what I have seem and heard in the pits at meetings 80 % of NZCMRR bikes are too rich and too advanced. The size of mains some people say they use are incredible.
Based on this Jennings paper in about an hour I changed my clubmans bike from petrol to methanol . Adjusted the ignition by looking at the plug from two test runs and ran it in the 2009 or 10 ?? 500 Senior TT. It came second with a one minute 11.2 sec lap of Puke.
So if you dont have a dyno then read this paper several times , buy a magnifying glass and a box of new plugs and try testing. Jennings really knows what he is talking about.
Last thing. I like your use of Commando mufflers. I tested hollow ones on a dyno with my bike and they gave nearly the same performance as a full race megaphone system - just a bit heavy. Plus you might want to try cutting off a bit of the reverse cone.
good luck
John